/**
  * Created by ruslan on 3/29/17.
  */
object ProblemA extends App {
    import java.io.{BufferedReader, IOException, InputStreamReader, PrintWriter}
import java.util.StringTokenizer

import scala.collection.mutable
import scala.util.Random
  val in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)))
  val out = new PrintWriter(System.out)

class  FastScanner(val in: BufferedReader) {
  var st: StringTokenizer = _;

  def nextToken(): String = {
    while (st == null || !st.hasMoreTokens()) {
        st = new StringTokenizer(in.readLine);
    }
    return st.nextToken();
  }

  def nextInt(): Integer = {
    Integer.parseInt(nextToken());
  }

  def nextLong(): Long = {
    nextToken().toLong;
  }

  def nextDouble(): Double = {
    nextToken().toDouble;
  }
}

  val startTime = System.currentTimeMillis();

  val n = in.nextInt();
  val a = new Array[Int](n)
  for (i <- 0 until n) a(i) = in.nextInt()

  var sums0 = new Array[(Long, Int)](n)
  var sums1 = new Array[(Long, Int)](n)

  sums0(0) = (0, 0)
  sums1(0) = (0, 0)

  for (i <- 1 until n) {
    val delta = Math.abs(a(i) - a(i - 1));
    sums0(i) = (sums0(i - 1)._1 + delta * (if (i % 2 == 0) -1 else 1), i)
    sums1(i) = (sums1(i - 1)._1 + delta * (if (i % 2 == 1) -1 else 1), i)
  }

  var res = Long.MinValue

  sums0 = sums0.sortWith(_._1 < _._1)
  sums1 = sums1.sortWith(_._1 < _._1)

  for(i <- n - 1 to 0 by -1) {
    val del1 = Math.abs(sums0(i)._1 - sums0(0)._1)
    val del2 = Math.abs(sums1(i)._1 - sums1(0)._1)
    if (del1 > res) res = del1
    if (del2 > res) res = del2
  }

  println(res)

}

object _789C extends CodeForcesApp {
  import Utils._, annotation._, collection.{mutable, Searching}, util._, control._, math.Ordering.Implicits._, Searching._

  override def apply(io: IO) = {import io.{read, readAll, write, writeAll, writeLine}
    val array = read[Vector[Long]]
    val diffs = array
      .zip(array.tail)
      .zipWithIndex
      .map({case ((a, b), i) =>
        val d = (a - b).abs
        val isEven = i%2 == 0
        (if (isEven) d else -d, if (isEven) -d else d)
      })
      .unzip
      .toSeq

    val ans = diffs.map(maxSubArraySum)

    write(ans.max)
  }

  def maxSubArraySum(s: Seq[Long]): Long = s.scanLeft(0L){_ + _ max 0L}.max

}
/****************************[Ignore Template Below]****************************************/
trait CodeForcesApp {
  lazy val isOnlineJudge: Boolean = sys.props.get("ONLINE_JUDGE").exists(_.toBoolean)
  def debug(x: => Any): Unit = if (!isOnlineJudge) println(x)
  def apply(io: IO): io.type
  def main(args: Array[String]): Unit = this(new IO(System.in, System.out)).close()
}
object Utils {
  import scala.collection.mutable, mutable.{Map => Dict}
  implicit class GenericExtensions[A](val a: A) extends AnyVal {
    def in(set: collection.Set[A]): Boolean = set(a)
    def some: Option[A] = Some(a)
    def partialMatch[B](f: PartialFunction[A, B]): Option[B] = f lift a
  }
  implicit class TraversableExtensions[A, C[X] <: Traversable[X]](val t: C[A]) extends AnyVal {
    def onlyElement: A = assuming(t.size == 1)(t.head)
    def groupByIdentifier[K](f: A => K): Map[K, A] = t.groupBy(f).mapValues(_.onlyElement)
    def duplicates(implicit b: C of A): C[A] = {
      val elems = mutable.Set.empty[A]
      (t collect {case i if !elems.add(i) => i}).to[C]
    }
    def sumWith[B](f: A => B)(implicit n: Numeric[B]): B = t.foldLeft(n.zero) {case (p, i) => n.plus(p, f(i))}
    def maxWith[B](f: A => B)(implicit ord: Ordering[B]): Option[B] = t.view.map(f).reduceOption(ord.max)
    def minWith[B](f: A => B)(implicit ord: Ordering[B]): Option[B] = t.view.map(f).reduceOption(ord.min)
    def zipWith[B](f: A => B)(implicit b: C of (A, B)): C[(A, B)] = (t map {i => i -> f(i)}).to[C]
    def mapTo[B](f: A => B)(implicit b: C of (A, B)): Map[A, B] = zipWith(f).toUniqueMap
    def whenNonEmpty[B](f: t.type => B): Option[B] = when(t.nonEmpty)(f(t))  // e.g. grades.whenNonEmpty(_.max)
    def collectFirst[B](f: PartialFunction[A, Option[B]]): Option[B] = t.view collect f collectFirst {case Some(x) => x}
    def toMutableMultiSet: Dict[A, Int] = {
      val c = map[A] to 0
      t.foreach(i => c(i) += 1)
      c
    }
    def toMultiSet: Map[A, Int] = toMutableMultiSet.toMap withDefaultValue 0
    def X[B](s: Traversable[B]): Iterator[(A, B)] = for {a <- t.toIterator; b <- s} yield (a, b)
  }
  implicit class ArrayExtensions[A <: AnyRef](val a: Array[A]) extends AnyVal {
    def sort(from: Int, until: Int)(implicit cmp: Ordering[A]): Unit = java.util.Arrays.sort(a, from, until, cmp) //sort [from, until)
  }
  implicit class ArrayExtensions2[A](val a: Array[A]) extends AnyVal {
    def sort(from: Int, until: Int)(implicit cmp: Ordering[A]): Unit = a.view(from, until).sorted.copyToArray(a, from)
  }
  implicit class SeqExtensions[A, C[X] <: Seq[X]](val s: C[A]) extends AnyVal {
    def isRotationOf(t: Seq[A]): Boolean = s ++ s containsSlice t
  }
  implicit class PairExtensions[A, B](val p: (A, B)) extends AnyVal {
    def key = p._1
    def value = p._2
    def toSeq(implicit ev: A =:= B): Seq[A] = Seq(p._1, p._2.asInstanceOf[A])
  }
  implicit class PairsExtensions[A, B, C[X] <: Traversable[X]](t: C[(A, B)]) {
    def toUniqueMap: Map[A, B] = t.groupByIdentifier(_.key).mapValues(_.value)
    def toMultiMap(implicit b: C of B): Map[A, C[B]] = t.groupBy(_.key).mapValues(_.map(_.value).to[C])
    def swap(implicit b: C of (B, A)): C[(B, A)] = t.map(_.swap).to[C]
  }
  implicit class MapExtensions[K, V, C[X, Y] <: Map[X, Y]](val m: C[K, V]) extends AnyVal {
    def lastKeyOption: Option[K] = m.lastOption.map(_.key)
    def firstKeyOption: Option[K] = m.headOption.map(_.key)
    def invert: Map[V, Set[K]] = m.toSet[(K, V)].swap.toMultiMap
    def mapKeys[K2](f: K => K2): Map[K2, V] = m map {case (k, v) => f(k) -> v}
    def toMutable: Dict[K, V] = Dict.empty[K, V] ++ m
    def mapValuesSafely[V2](f: V => V2): Map[K, V2] = m.mapValues(f).view.force //Hack to get around https://issues.scala-lang.org/browse/SI-4776
  }
  implicit class MutableMapExtensions[K, V](val m: mutable.Map[K, V]) extends AnyVal {
    def removeLast(): Option[(K, V)] = m.lastOption.map(removeNode)
    def removeFirst(): Option[(K, V)] = m.headOption.map(removeNode)
    private def removeNode(kv: (K, V)): (K, V) = {
      m -= kv.key
      kv
    }
  }
  implicit class SetExtensions[A, C[A] <: Set[A]](val s: C[A]) extends AnyVal {
    def notContains(x: A): Boolean = !(s contains x)
    def toMutable = mutable.Set.empty[A] ++ s
  }
  implicit class IterableExtensions[A, C[A] <: Seq[A]](val s: C[A]) extends AnyVal {
    def indicesWhere(f: A => Boolean): Seq[Int] = s.zipWithIndex.collect {case (a, i) if f(a) => i}
    def deleteAtIndex(i: Int, howMany: Int = 1) = s.patch(i, Nil, howMany)
    def insertAtIndex(i: Int, items: Seq[A]) = s.patch(i, items, 0)
    def findWithIndex(f: A => Boolean): Option[(A, Int)] = s.zipWithIndex find {case (a, _) => f(a)}
    def foldUntil[B](z: B)(f: (B, A) => B)(c: B => Boolean): Option[(B, Int)] = s.view.scanLeft(z)(f).findWithIndex(c)
  }
  implicit class BooleanExtensions(val x: Boolean) extends AnyVal {
    def to[A](implicit n: Numeric[A]) = if(x) n.one else n.zero
    def toEnglish = if(x) "YES" else "NO"
  }
  implicit class IntExtensions(val x: Int) extends AnyVal {
    import java.lang.{Integer => JInt}
    def withHighestOneBit: Int = JInt.highestOneBit(x)
    def withLowestOneBit: Int = JInt.lowestOneBit(x)
    def numberOfLeadingZeroes: Int = JInt.numberOfLeadingZeros(x)
    def numberOfTrailingZeroes: Int = JInt.numberOfTrailingZeros(x)
    def bitCount: Int = JInt.bitCount(x)
    def setLowestBits(n: Int): Int = x | (left(n) - 1)
    def clearLowestBits(n: Int): Int = x & left(n, ~0)
    def setBit(i: Int, set: Boolean): Int = if (set) setBit(i) else clearBit(i)
    def setBit(i: Int): Int = x | left(i)
    def clearBit(i: Int): Int = x & ~left(i)
    def toggleBit(i: Int): Int = x ^ left(i)
    def testBit(i: Int): Boolean = ((x >> i) & 1) == 1
    private def left(bits: Int, num: Int = 1) = assuming(bits >= 0 && bits < JInt.SIZE)(num << bits)
    def X(y: Int): Iterator[(Int, Int)] = until(x) X until(y)
  }
  implicit class LongExtensions(val x: Long) extends AnyVal {
    import java.lang.{Long => JLong}
    def withHighestOneBitSet: Long = JLong.highestOneBit(x)
    def withLowestOneBitSet: Long = JLong.lowestOneBit(x)
    def numberOfLeadingZeroes: Int = JLong.numberOfLeadingZeros(x)
    def numberOfTrailingZeroes: Int = JLong.numberOfTrailingZeros(x)
    def bitCount: Int = JLong.bitCount(x)
    def setLowestBits(n: Int): Long = x | (left(n) - 1)
    def clearLowestBits(n: Int): Long = x & left(n, ~0L)
    def setBit(i: Int, set: Boolean): Long = if (set) setBit(i) else clearBit(i)
    def setBit(i: Int): Long = x | left(i)
    def clearBit(i: Int): Long = x & ~left(i)
    def toggleBit(i: Int): Long = x ^ left(i)
    def testBit(i: Int): Boolean = ((x >> i) & 1) == 1
    private def left(bits: Int, num: Long = 1L) = assuming(bits >= 0 && bits < JLong.SIZE)(num << bits)
  }
  implicit class NumericExtensions[A](val x: A)(implicit n: Numeric[A]) {
    import Numeric.Implicits._
    def **(i: Int): A = if (i == 0) n.one else {
      val h = x ** (i/2)
      if (i%2 == 0) h * h else h * h * x
    }
    def distance(y: A) = (x - y).abs()
    def nonNegative: Option[A] = when(n.gteq(x, n.zero))(x)
    def whenNegative(f: => A): A = nonNegative getOrElse f   //e.g. students indexOf "Greg" whenNegative Int.MaxValue
  }
  implicit class IntegralExtensions[A](val x: A)(implicit n: Integral[A]) {
    import scala.collection.immutable.NumericRange, Integral.Implicits._
    def mod(y: A): A = x - ((x / y) * y) //(x/y)*y + (x mod y) == x
    def -->(y: A): NumericRange.Inclusive[A] = NumericRange.inclusive(x, y, if (n.lteq(x, y)) n.one else -n.one)
    def ceilDiv(y: A): A = if (mod(y) == n.zero) x/y else n.one + (x/y)
  }
  implicit def toPoint[A](p: (A, A))(implicit n: Numeric[A]) = new java.awt.geom.Point2D.Double(n.toDouble(p._1), n.toDouble(p._2))
  def desc[A: Ordering]: Ordering[A] = asc[A].reverse  //e.g. students.sortBy(_.height)(desc)
  def asc[A](implicit order: Ordering[A]): Ordering[A] = order
  def map[K] = new {
    def to[V](default: => V): Dict[K, V] = using(_ => default)
    def using[V](f: K => V): Dict[K, V] = new mutable.HashMap[K, V]() {
      override def apply(key: K) = getOrElseUpdate(key, f(key))
    }
  }
  def newMultiMap[K, V] = map[K] to mutable.Set.empty[V]
  def memoize[A, B](f: A => B): A ==> B = map[A] using f
  implicit class FuzzyDouble(val x: Double) extends AnyVal {
    def  >~(y: Double) = x > y + eps
    def >=~(y: Double) = x >= y + eps
    def  ~<(y: Double) = y >=~ x
    def ~=<(y: Double) = y >~ x
    def  ~=(y: Double) = (x distance y) <= eps
  }
  def toPolygon(points: Traversable[(Int, Int)]): java.awt.Polygon = {
    val (xs, ys) = points.unzip
    new java.awt.Polygon(xs.toArray, ys.toArray, points.size)
  }
  def toShape(points: Traversable[(Double, Double)]): java.awt.geom.GeneralPath = {
    val shape = new java.awt.geom.GeneralPath()
    points.headOption foreach {case (x, y) => shape.moveTo(x, y)}
    points.tail foreach {case (x, y) => shape.lineTo(x, y)}
    shape.closePath()
    shape
  }
  def until(until: Int): Range = 0 until until
  def not[A](f: A => Boolean): A => Boolean = {x: A => !f(x)}
  def assuming[A](cond: => Boolean)(f: => A): A = {require(cond); f}
  @inline def when[A](check: Boolean)(f: => A): Option[A] = if (check) f.some else None
  def repeat[U](n: Int)(f: => U): Unit = (1 to n).foreach(_ => f)
  type of[C[_], A] = scala.collection.generic.CanBuild[A, C[A]]
  type ==>[A, B] = collection.Map[A, B]
  val mod: Int = (1e9 + 7).toInt
  val eps: Double = 1e-9
}
/***********************************[Scala I/O]*********************************************/
import Utils._, java.io._, java.util.StringTokenizer

class IO(in: BufferedReader, out: BufferedWriter) extends Iterator[String] with AutoCloseable with Flushable {
  def this(reader: Reader, writer: Writer) = this(new BufferedReader(reader), new BufferedWriter(writer))
  def this(in: InputStream, out: OutputStream) = this(new InputStreamReader(in), new OutputStreamWriter(out))

  private[this] val tokenizers = Iterator.continually(in.readLine()).takeWhile(_ != null).map(new StringTokenizer(_)).buffered
  val printer = new PrintWriter(out, true)

  @inline private[this] def tokenizer() = {
    while(tokenizers.nonEmpty && !tokenizers.head.hasMoreTokens) tokenizers.next()
    when(tokenizers.nonEmpty)(tokenizers.head)
  }

  def read[A](implicit read: IO.Read[A]): A = read.apply(this)
  def read[C[_], A: IO.Read](n: Int)(implicit b: C of A): C[A] = Iterator.fill(n)(read).to[C]

  def readTill(delim: String): String = tokenizer().get.nextToken(delim)
  def readTillEndOfLine(): String = readTill("\n\r")

  def readAll[A: IO.Read]: (Int, Vector[A]) = {
    val data = read[Vector[A]]
    (data.length, data)
  }

  override def next() = tokenizer().get.nextToken()
  override def hasNext = tokenizer().nonEmpty

  def write(obj: Any): this.type = {
    printer.print(obj)
    this
  }
  def writeLine(): this.type = {
    printer.println()
    this
  }
  def writeLine(obj: Any): this.type = {
    printer.println(obj)
    this
  }
  def writeAll(obj: Traversable[Any], separator: String = " "): this.type = write(obj mkString separator)
  def query[A: IO.Read](question: Any): A = writeLine(question).read

  override def flush() = printer.flush()
  def close() = {
    flush()
    in.close()
    printer.close()
  }
}
object IO {
  class Read[A](val apply: IO => A) {
    def map[B](f: A => B): Read[B] = new Read(apply andThen f)
  }
  object Read {
    implicit def collection[C[_], A: Read](implicit b: C of A): Read[C[A]]         = new Read(r => r.read[C, A](r.read[Int]))
    implicit val string                                       : Read[String]       = new Read(_.next())
    implicit val char                                         : Read[Char]         = string.map(_.toTraversable.onlyElement)
    implicit val int                                          : Read[Int]          = string.map(_.toInt)
    implicit val long                                         : Read[Long]         = string.map(_.toLong)
    implicit val bigInt                                       : Read[BigInt]       = string.map(BigInt(_))
    implicit val double                                       : Read[Double]       = string.map(_.toDouble)
    implicit val bigDecimal                                   : Read[BigDecimal]   = string.map(BigDecimal(_))
    implicit def tuple2[A: Read, B: Read]                     : Read[(A, B)]       = new Read(r => (r.read[A], r.read[B]))
    implicit def tuple3[A: Read, B: Read, C: Read]            : Read[(A, B, C)]    = new Read(r => (r.read[A], r.read[B], r.read[C]))
    implicit def tuple4[A: Read, B: Read, C: Read, D: Read]   : Read[(A, B, C, D)] = new Read(r => (r.read[A], r.read[B], r.read[C], r.read[D]))
    implicit val boolean                                      : Read[Boolean]      = string map {s =>
      s.toLowerCase match {
        case "yes" | "true" | "1" => true
        case "no" | "false" | "0" => false
        case _ => s.toBoolean
      }
    }
  }
}

object _789C extends CodeForcesApp {
  import Utils._, annotation._, collection.{mutable, Searching}, util._, control._, math.Ordering.Implicits._, Searching._

  override def apply(io: IO) = {import io.{read, readAll, write, writeAll, writeLine}
    val array = read[Vector[Long]]
    val diffs = array.view
      .zip(array.tail)
      .zipWithIndex
      .map({case ((a, b), i) =>
        val d = (a - b).abs
        val isEven = i%2 == 0
        (if (isEven) d else -d, if (isEven) -d else d)
      })
      .force
      .unzip
      .toSeq

    val ans = diffs.map(maxSubArraySum)
    write(ans.max)
  }

  def maxSubArraySum(s: Seq[Long]): Long = s.scanLeft(0L){_ + _ max 0L}.max
}
/****************************[Ignore Template Below]****************************************/
trait CodeForcesApp {
  lazy val isOnlineJudge: Boolean = sys.props.get("ONLINE_JUDGE").exists(_.toBoolean)
  def debug(x: => Any): Unit = if (!isOnlineJudge) println(x)
  def apply(io: IO): io.type
  def main(args: Array[String]): Unit = this(new IO(System.in, System.out)).close()
}
object Utils {
  import scala.collection.mutable, mutable.{Map => Dict}
  implicit class GenericExtensions[A](val a: A) extends AnyVal {
    def in(set: collection.Set[A]): Boolean = set(a)
    def some: Option[A] = Some(a)
    def partialMatch[B](f: PartialFunction[A, B]): Option[B] = f lift a
  }
  implicit class TraversableExtensions[A, C[X] <: Traversable[X]](val t: C[A]) extends AnyVal {
    def onlyElement: A = assuming(t.size == 1)(t.head)
    def groupByIdentifier[K](f: A => K): Map[K, A] = t.groupBy(f).mapValues(_.onlyElement)
    def duplicates(implicit b: C of A): C[A] = {
      val elems = mutable.Set.empty[A]
      (t collect {case i if !elems.add(i) => i}).to[C]
    }
    def sumWith[B](f: A => B)(implicit n: Numeric[B]): B = t.foldLeft(n.zero) {case (p, i) => n.plus(p, f(i))}
    def maxWith[B](f: A => B)(implicit ord: Ordering[B]): Option[B] = t.view.map(f).reduceOption(ord.max)
    def minWith[B](f: A => B)(implicit ord: Ordering[B]): Option[B] = t.view.map(f).reduceOption(ord.min)
    def zipWith[B](f: A => B)(implicit b: C of (A, B)): C[(A, B)] = (t map {i => i -> f(i)}).to[C]
    def mapTo[B](f: A => B)(implicit b: C of (A, B)): Map[A, B] = zipWith(f).toUniqueMap
    def whenNonEmpty[B](f: t.type => B): Option[B] = when(t.nonEmpty)(f(t))  // e.g. grades.whenNonEmpty(_.max)
    def collectFirst[B](f: PartialFunction[A, Option[B]]): Option[B] = t.view collect f collectFirst {case Some(x) => x}
    def toMutableMultiSet: Dict[A, Int] = {
      val c = map[A] to 0
      t.foreach(i => c(i) += 1)
      c
    }
    def toMultiSet: Map[A, Int] = toMutableMultiSet.toMap withDefaultValue 0
    def X[B](s: Traversable[B]): Iterator[(A, B)] = for {a <- t.toIterator; b <- s} yield (a, b)
  }
  implicit class ArrayExtensions[A <: AnyRef](val a: Array[A]) extends AnyVal {
    def sort(from: Int, until: Int)(implicit cmp: Ordering[A]): Unit = java.util.Arrays.sort(a, from, until, cmp) //sort [from, until)
  }
  implicit class ArrayExtensions2[A](val a: Array[A]) extends AnyVal {
    def sort(from: Int, until: Int)(implicit cmp: Ordering[A]): Unit = a.view(from, until).sorted.copyToArray(a, from)
  }
  implicit class SeqExtensions[A, C[X] <: Seq[X]](val s: C[A]) extends AnyVal {
    def isRotationOf(t: Seq[A]): Boolean = s ++ s containsSlice t
  }
  implicit class PairExtensions[A, B](val p: (A, B)) extends AnyVal {
    def key = p._1
    def value = p._2
    def toSeq(implicit ev: A =:= B): Seq[A] = Seq(p._1, p._2.asInstanceOf[A])
  }
  implicit class PairsExtensions[A, B, C[X] <: Traversable[X]](t: C[(A, B)]) {
    def toUniqueMap: Map[A, B] = t.groupByIdentifier(_.key).mapValues(_.value)
    def toMultiMap(implicit b: C of B): Map[A, C[B]] = t.groupBy(_.key).mapValues(_.map(_.value).to[C])
    def swap(implicit b: C of (B, A)): C[(B, A)] = t.map(_.swap).to[C]
  }
  implicit class MapExtensions[K, V, C[X, Y] <: Map[X, Y]](val m: C[K, V]) extends AnyVal {
    def lastKeyOption: Option[K] = m.lastOption.map(_.key)
    def firstKeyOption: Option[K] = m.headOption.map(_.key)
    def invert: Map[V, Set[K]] = m.toSet[(K, V)].swap.toMultiMap
    def mapKeys[K2](f: K => K2): Map[K2, V] = m map {case (k, v) => f(k) -> v}
    def toMutable: Dict[K, V] = Dict.empty[K, V] ++ m
    def mapValuesSafely[V2](f: V => V2): Map[K, V2] = m.mapValues(f).view.force //Hack to get around https://issues.scala-lang.org/browse/SI-4776
  }
  implicit class MutableMapExtensions[K, V](val m: mutable.Map[K, V]) extends AnyVal {
    def removeLast(): Option[(K, V)] = m.lastOption.map(removeNode)
    def removeFirst(): Option[(K, V)] = m.headOption.map(removeNode)
    private def removeNode(kv: (K, V)): (K, V) = {
      m -= kv.key
      kv
    }
  }
  implicit class SetExtensions[A, C[A] <: Set[A]](val s: C[A]) extends AnyVal {
    def notContains(x: A): Boolean = !(s contains x)
    def toMutable = mutable.Set.empty[A] ++ s
  }
  implicit class IterableExtensions[A, C[A] <: Seq[A]](val s: C[A]) extends AnyVal {
    def indicesWhere(f: A => Boolean): Seq[Int] = s.zipWithIndex.collect {case (a, i) if f(a) => i}
    def deleteAtIndex(i: Int, howMany: Int = 1) = s.patch(i, Nil, howMany)
    def insertAtIndex(i: Int, items: Seq[A]) = s.patch(i, items, 0)
    def findWithIndex(f: A => Boolean): Option[(A, Int)] = s.zipWithIndex find {case (a, _) => f(a)}
    def foldUntil[B](z: B)(f: (B, A) => B)(c: B => Boolean): Option[(B, Int)] = s.view.scanLeft(z)(f).findWithIndex(c)
  }
  implicit class BooleanExtensions(val x: Boolean) extends AnyVal {
    def to[A](implicit n: Numeric[A]) = if(x) n.one else n.zero
    def toEnglish = if(x) "YES" else "NO"
  }
  implicit class IntExtensions(val x: Int) extends AnyVal {
    import java.lang.{Integer => JInt}
    def withHighestOneBit: Int = JInt.highestOneBit(x)
    def withLowestOneBit: Int = JInt.lowestOneBit(x)
    def numberOfLeadingZeroes: Int = JInt.numberOfLeadingZeros(x)
    def numberOfTrailingZeroes: Int = JInt.numberOfTrailingZeros(x)
    def bitCount: Int = JInt.bitCount(x)
    def setLowestBits(n: Int): Int = x | (left(n) - 1)
    def clearLowestBits(n: Int): Int = x & left(n, ~0)
    def setBit(i: Int, set: Boolean): Int = if (set) setBit(i) else clearBit(i)
    def setBit(i: Int): Int = x | left(i)
    def clearBit(i: Int): Int = x & ~left(i)
    def toggleBit(i: Int): Int = x ^ left(i)
    def testBit(i: Int): Boolean = ((x >> i) & 1) == 1
    private def left(bits: Int, num: Int = 1) = assuming(bits >= 0 && bits < JInt.SIZE)(num << bits)
    def X(y: Int): Iterator[(Int, Int)] = until(x) X until(y)
  }
  implicit class LongExtensions(val x: Long) extends AnyVal {
    import java.lang.{Long => JLong}
    def withHighestOneBitSet: Long = JLong.highestOneBit(x)
    def withLowestOneBitSet: Long = JLong.lowestOneBit(x)
    def numberOfLeadingZeroes: Int = JLong.numberOfLeadingZeros(x)
    def numberOfTrailingZeroes: Int = JLong.numberOfTrailingZeros(x)
    def bitCount: Int = JLong.bitCount(x)
    def setLowestBits(n: Int): Long = x | (left(n) - 1)
    def clearLowestBits(n: Int): Long = x & left(n, ~0L)
    def setBit(i: Int, set: Boolean): Long = if (set) setBit(i) else clearBit(i)
    def setBit(i: Int): Long = x | left(i)
    def clearBit(i: Int): Long = x & ~left(i)
    def toggleBit(i: Int): Long = x ^ left(i)
    def testBit(i: Int): Boolean = ((x >> i) & 1) == 1
    private def left(bits: Int, num: Long = 1L) = assuming(bits >= 0 && bits < JLong.SIZE)(num << bits)
  }
  implicit class NumericExtensions[A](val x: A)(implicit n: Numeric[A]) {
    import Numeric.Implicits._
    def **(i: Int): A = if (i == 0) n.one else {
      val h = x ** (i/2)
      if (i%2 == 0) h * h else h * h * x
    }
    def distance(y: A) = (x - y).abs()
    def nonNegative: Option[A] = when(n.gteq(x, n.zero))(x)
    def whenNegative(f: => A): A = nonNegative getOrElse f   //e.g. students indexOf "Greg" whenNegative Int.MaxValue
  }
  implicit class IntegralExtensions[A](val x: A)(implicit n: Integral[A]) {
    import scala.collection.immutable.NumericRange, Integral.Implicits._
    def mod(y: A): A = x - ((x / y) * y) //(x/y)*y + (x mod y) == x
    def -->(y: A): NumericRange.Inclusive[A] = NumericRange.inclusive(x, y, if (n.lteq(x, y)) n.one else -n.one)
    def ceilDiv(y: A): A = if (mod(y) == n.zero) x/y else n.one + (x/y)
  }
  implicit def toPoint[A](p: (A, A))(implicit n: Numeric[A]) = new java.awt.geom.Point2D.Double(n.toDouble(p._1), n.toDouble(p._2))
  def desc[A: Ordering]: Ordering[A] = asc[A].reverse  //e.g. students.sortBy(_.height)(desc)
  def asc[A](implicit order: Ordering[A]): Ordering[A] = order
  def map[K] = new {
    def to[V](default: => V): Dict[K, V] = using(_ => default)
    def using[V](f: K => V): Dict[K, V] = new mutable.HashMap[K, V]() {
      override def apply(key: K) = getOrElseUpdate(key, f(key))
    }
  }
  def newMultiMap[K, V] = map[K] to mutable.Set.empty[V]
  def memoize[A, B](f: A => B): A ==> B = map[A] using f
  implicit class FuzzyDouble(val x: Double) extends AnyVal {
    def  >~(y: Double) = x > y + eps
    def >=~(y: Double) = x >= y + eps
    def  ~<(y: Double) = y >=~ x
    def ~=<(y: Double) = y >~ x
    def  ~=(y: Double) = (x distance y) <= eps
  }
  def toPolygon(points: Traversable[(Int, Int)]): java.awt.Polygon = {
    val (xs, ys) = points.unzip
    new java.awt.Polygon(xs.toArray, ys.toArray, points.size)
  }
  def toShape(points: Traversable[(Double, Double)]): java.awt.geom.GeneralPath = {
    val shape = new java.awt.geom.GeneralPath()
    points.headOption foreach {case (x, y) => shape.moveTo(x, y)}
    points.tail foreach {case (x, y) => shape.lineTo(x, y)}
    shape.closePath()
    shape
  }
  def until(until: Int): Range = 0 until until
  def not[A](f: A => Boolean): A => Boolean = {x: A => !f(x)}
  def assuming[A](cond: => Boolean)(f: => A): A = {require(cond); f}
  @inline def when[A](check: Boolean)(f: => A): Option[A] = if (check) f.some else None
  def repeat[U](n: Int)(f: => U): Unit = (1 to n).foreach(_ => f)
  type of[C[_], A] = scala.collection.generic.CanBuild[A, C[A]]
  type ==>[A, B] = collection.Map[A, B]
  val mod: Int = (1e9 + 7).toInt
  val eps: Double = 1e-9
}
/***********************************[Scala I/O]*********************************************/
import Utils._, java.io._, java.util.StringTokenizer

class IO(in: BufferedReader, out: BufferedWriter) extends Iterator[String] with AutoCloseable with Flushable {
  def this(reader: Reader, writer: Writer) = this(new BufferedReader(reader), new BufferedWriter(writer))
  def this(in: InputStream, out: OutputStream) = this(new InputStreamReader(in), new OutputStreamWriter(out))

  private[this] val tokenizers = Iterator.continually(in.readLine()).takeWhile(_ != null).map(new StringTokenizer(_)).buffered
  val printer = new PrintWriter(out, true)

  @inline private[this] def tokenizer() = {
    while(tokenizers.nonEmpty && !tokenizers.head.hasMoreTokens) tokenizers.next()
    when(tokenizers.nonEmpty)(tokenizers.head)
  }

  def read[A](implicit read: IO.Read[A]): A = read.apply(this)
  def read[C[_], A: IO.Read](n: Int)(implicit b: C of A): C[A] = Iterator.fill(n)(read).to[C]

  def readTill(delim: String): String = tokenizer().get.nextToken(delim)
  def readTillEndOfLine(): String = readTill("\n\r")

  def readAll[A: IO.Read]: (Int, Vector[A]) = {
    val data = read[Vector[A]]
    (data.length, data)
  }

  override def next() = tokenizer().get.nextToken()
  override def hasNext = tokenizer().nonEmpty

  def write(obj: Any): this.type = {
    printer.print(obj)
    this
  }
  def writeLine(): this.type = {
    printer.println()
    this
  }
  def writeLine(obj: Any): this.type = {
    printer.println(obj)
    this
  }
  def writeAll(obj: Traversable[Any], separator: String = " "): this.type = write(obj mkString separator)
  def query[A: IO.Read](question: Any): A = writeLine(question).read

  override def flush() = printer.flush()
  def close() = {
    flush()
    in.close()
    printer.close()
  }
}
object IO {
  class Read[A](val apply: IO => A) {
    def map[B](f: A => B): Read[B] = new Read(apply andThen f)
  }
  object Read {
    implicit def collection[C[_], A: Read](implicit b: C of A): Read[C[A]]         = new Read(r => r.read[C, A](r.read[Int]))
    implicit val string                                       : Read[String]       = new Read(_.next())
    implicit val char                                         : Read[Char]         = string.map(_.toTraversable.onlyElement)
    implicit val int                                          : Read[Int]          = string.map(_.toInt)
    implicit val long                                         : Read[Long]         = string.map(_.toLong)
    implicit val bigInt                                       : Read[BigInt]       = string.map(BigInt(_))
    implicit val double                                       : Read[Double]       = string.map(_.toDouble)
    implicit val bigDecimal                                   : Read[BigDecimal]   = string.map(BigDecimal(_))
    implicit def tuple2[A: Read, B: Read]                     : Read[(A, B)]       = new Read(r => (r.read[A], r.read[B]))
    implicit def tuple3[A: Read, B: Read, C: Read]            : Read[(A, B, C)]    = new Read(r => (r.read[A], r.read[B], r.read[C]))
    implicit def tuple4[A: Read, B: Read, C: Read, D: Read]   : Read[(A, B, C, D)] = new Read(r => (r.read[A], r.read[B], r.read[C], r.read[D]))
    implicit val boolean                                      : Read[Boolean]      = string map {s =>
      s.toLowerCase match {
        case "yes" | "true" | "1" => true
        case "no" | "false" | "0" => false
        case _ => s.toBoolean
      }
    }
  }
}

object ProblemA extends App {

    import java.io.{BufferedReader, IOException, InputStreamReader, PrintWriter}
    import java.util.StringTokenizer

  val in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)))
  val out = new PrintWriter(System.out)

  val startTime = System.currentTimeMillis();

  val n = in.nextInt();
  val a = new Array[Int](n)
  for (i <- 0 until n) a(i) = in.nextInt()

  var sums0 = new Array[(Long, Int)](n)
  var sums1 = new Array[(Long, Int)](n)

  sums0(0) = (0, 0)
  sums1(0) = (0, 0)

  for (i <- 1 until n) {
    val delta = Math.abs(a(i) - a(i - 1));
    sums0(i) = (sums0(i - 1)._1 + delta * (if (i % 2 == 0) -1 else 1), i)
    sums1(i) = (sums1(i - 1)._1 + delta * (if (i % 2 == 1) -1 else 1), i)
  }

  var res = Long.MinValue

  sums0 = sums0.sortWith(_._1 < _._1)
  sums1 = sums1.sortWith(_._1 < _._1)

  for(i <- n - 1 to 0 by -1) {
    val del1 = Math.abs(sums0(i)._1 - sums0(0)._1)
    val del2 = Math.abs(sums1(i)._1 - sums1(0)._1)
    if (del1 > res) res = del1
    if (del2 > res) res = del2
  }

  println(res)

}

import java.io.{BufferedReader, IOException, InputStreamReader, PrintWriter}
import java.util.StringTokenizer

class  FastScanner(val in: BufferedReader) {

  var st: StringTokenizer = _;

  def nextToken(): String = {
    while (st == null || !st.hasMoreTokens()) {
        st = new StringTokenizer(in.readLine);
    }
    return st.nextToken();
  }

  def nextInt(): Integer = {
    Integer.parseInt(nextToken());
  }

  def nextLong(): Long = {
    nextToken().toLong;
  }

  def nextDouble(): Double = {
    nextToken().toDouble;
  }
}

object _789C extends CodeForcesApp {
  import Utils._, annotation._, collection.{mutable, Searching}, util._, control._, math.Ordering.Implicits._, Searching._

  override def apply(io: IO) = {import io.{read, readAll, write, writeAll, writeLine}
    val array = read[Vector[Long]]
    val diffs = array
      .zip(array.tail)
      .map({case (a, b) => (a - b, b - a)})
    val (c1, c2) = diffs.unzip
    val ans = maxSubArraySum(c1) max maxSubArraySum(c2)
    write(ans)
  }

  def maxSubArraySum(s: Seq[Long]): Long = s.scanLeft(0L){_ + _ max 0L}.max

}
/****************************[Ignore Template Below]****************************************/
trait CodeForcesApp {
  lazy val isOnlineJudge: Boolean = sys.props.get("ONLINE_JUDGE").exists(_.toBoolean)
  def debug(x: => Any): Unit = if (!isOnlineJudge) println(x)
  def apply(io: IO): io.type
  def main(args: Array[String]): Unit = this(new IO(System.in, System.out)).close()
}
object Utils {
  import scala.collection.mutable, mutable.{Map => Dict}
  implicit class GenericExtensions[A](val a: A) extends AnyVal {
    def in(set: collection.Set[A]): Boolean = set(a)
    def some: Option[A] = Some(a)
    def partialMatch[B](f: PartialFunction[A, B]): Option[B] = f lift a
  }
  implicit class TraversableExtensions[A, C[X] <: Traversable[X]](val t: C[A]) extends AnyVal {
    def onlyElement: A = assuming(t.size == 1)(t.head)
    def groupByIdentifier[K](f: A => K): Map[K, A] = t.groupBy(f).mapValues(_.onlyElement)
    def duplicates(implicit b: C of A): C[A] = {
      val elems = mutable.Set.empty[A]
      (t collect {case i if !elems.add(i) => i}).to[C]
    }
    def sumWith[B](f: A => B)(implicit n: Numeric[B]): B = t.foldLeft(n.zero) {case (p, i) => n.plus(p, f(i))}
    def maxWith[B](f: A => B)(implicit ord: Ordering[B]): Option[B] = t.view.map(f).reduceOption(ord.max)
    def minWith[B](f: A => B)(implicit ord: Ordering[B]): Option[B] = t.view.map(f).reduceOption(ord.min)
    def zipWith[B](f: A => B)(implicit b: C of (A, B)): C[(A, B)] = (t map {i => i -> f(i)}).to[C]
    def mapTo[B](f: A => B)(implicit b: C of (A, B)): Map[A, B] = zipWith(f).toUniqueMap
    def whenNonEmpty[B](f: t.type => B): Option[B] = when(t.nonEmpty)(f(t))  // e.g. grades.whenNonEmpty(_.max)
    def collectFirst[B](f: PartialFunction[A, Option[B]]): Option[B] = t.view collect f collectFirst {case Some(x) => x}
    def toMutableMultiSet: Dict[A, Int] = {
      val c = map[A] to 0
      t.foreach(i => c(i) += 1)
      c
    }
    def toMultiSet: Map[A, Int] = toMutableMultiSet.toMap withDefaultValue 0
    def X[B](s: Traversable[B]): Iterator[(A, B)] = for {a <- t.toIterator; b <- s} yield (a, b)
  }
  implicit class ArrayExtensions[A <: AnyRef](val a: Array[A]) extends AnyVal {
    def sort(from: Int, until: Int)(implicit cmp: Ordering[A]): Unit = java.util.Arrays.sort(a, from, until, cmp) //sort [from, until)
  }
  implicit class ArrayExtensions2[A](val a: Array[A]) extends AnyVal {
    def sort(from: Int, until: Int)(implicit cmp: Ordering[A]): Unit = a.view(from, until).sorted.copyToArray(a, from)
  }
  implicit class SeqExtensions[A, C[X] <: Seq[X]](val s: C[A]) extends AnyVal {
    def isRotationOf(t: Seq[A]): Boolean = s ++ s containsSlice t
  }
  implicit class PairExtensions[A, B](val p: (A, B)) extends AnyVal {
    def key = p._1
    def value = p._2
  }
  implicit class PairsExtensions[A, B, C[X] <: Traversable[X]](t: C[(A, B)]) {
    def toUniqueMap: Map[A, B] = t.groupByIdentifier(_.key).mapValues(_.value)
    def toMultiMap(implicit b: C of B): Map[A, C[B]] = t.groupBy(_.key).mapValues(_.map(_.value).to[C])
    def swap(implicit b: C of (B, A)): C[(B, A)] = t.map(_.swap).to[C]
  }
  implicit class MapExtensions[K, V, C[X, Y] <: Map[X, Y]](val m: C[K, V]) extends AnyVal {
    def lastKeyOption: Option[K] = m.lastOption.map(_.key)
    def firstKeyOption: Option[K] = m.headOption.map(_.key)
    def invert: Map[V, Set[K]] = m.toSet[(K, V)].swap.toMultiMap
    def mapKeys[K2](f: K => K2): Map[K2, V] = m map {case (k, v) => f(k) -> v}
    def toMutable: Dict[K, V] = Dict.empty[K, V] ++ m
    def mapValuesSafely[V2](f: V => V2): Map[K, V2] = m.mapValues(f).view.force //Hack to get around https://issues.scala-lang.org/browse/SI-4776
  }
  implicit class MutableMapExtensions[K, V](val m: mutable.Map[K, V]) extends AnyVal {
    def removeLast(): Option[(K, V)] = m.lastOption.map(removeNode)
    def removeFirst(): Option[(K, V)] = m.headOption.map(removeNode)
    private def removeNode(kv: (K, V)): (K, V) = {
      m -= kv.key
      kv
    }
  }
  implicit class SetExtensions[A, C[A] <: Set[A]](val s: C[A]) extends AnyVal {
    def notContains(x: A): Boolean = !(s contains x)
    def toMutable = mutable.Set.empty[A] ++ s
  }
  implicit class IterableExtensions[A, C[A] <: Seq[A]](val s: C[A]) extends AnyVal {
    def indicesWhere(f: A => Boolean): Seq[Int] = s.zipWithIndex.collect {case (a, i) if f(a) => i}
    def deleteAtIndex(i: Int, howMany: Int = 1) = s.patch(i, Nil, howMany)
    def insertAtIndex(i: Int, items: Seq[A]) = s.patch(i, items, 0)
    def findWithIndex(f: A => Boolean): Option[(A, Int)] = s.zipWithIndex find {case (a, _) => f(a)}
    def foldUntil[B](z: B)(f: (B, A) => B)(c: B => Boolean): Option[(B, Int)] = s.view.scanLeft(z)(f).findWithIndex(c)
  }
  implicit class BooleanExtensions(val x: Boolean) extends AnyVal {
    def to[A](implicit n: Numeric[A]) = if(x) n.one else n.zero
    def toEnglish = if(x) "YES" else "NO"
  }
  implicit class IntExtensions(val x: Int) extends AnyVal {
    import java.lang.{Integer => JInt}
    def withHighestOneBit: Int = JInt.highestOneBit(x)
    def withLowestOneBit: Int = JInt.lowestOneBit(x)
    def numberOfLeadingZeroes: Int = JInt.numberOfLeadingZeros(x)
    def numberOfTrailingZeroes: Int = JInt.numberOfTrailingZeros(x)
    def bitCount: Int = JInt.bitCount(x)
    def setLowestBits(n: Int): Int = x | (left(n) - 1)
    def clearLowestBits(n: Int): Int = x & left(n, ~0)
    def setBit(i: Int, set: Boolean): Int = if (set) setBit(i) else clearBit(i)
    def setBit(i: Int): Int = x | left(i)
    def clearBit(i: Int): Int = x & ~left(i)
    def toggleBit(i: Int): Int = x ^ left(i)
    def testBit(i: Int): Boolean = ((x >> i) & 1) == 1
    private def left(bits: Int, num: Int = 1) = assuming(bits >= 0 && bits < JInt.SIZE)(num << bits)
    def X(y: Int): Iterator[(Int, Int)] = until(x) X until(y)
  }
  implicit class LongExtensions(val x: Long) extends AnyVal {
    import java.lang.{Long => JLong}
    def withHighestOneBitSet: Long = JLong.highestOneBit(x)
    def withLowestOneBitSet: Long = JLong.lowestOneBit(x)
    def numberOfLeadingZeroes: Int = JLong.numberOfLeadingZeros(x)
    def numberOfTrailingZeroes: Int = JLong.numberOfTrailingZeros(x)
    def bitCount: Int = JLong.bitCount(x)
    def setLowestBits(n: Int): Long = x | (left(n) - 1)
    def clearLowestBits(n: Int): Long = x & left(n, ~0L)
    def setBit(i: Int, set: Boolean): Long = if (set) setBit(i) else clearBit(i)
    def setBit(i: Int): Long = x | left(i)
    def clearBit(i: Int): Long = x & ~left(i)
    def toggleBit(i: Int): Long = x ^ left(i)
    def testBit(i: Int): Boolean = ((x >> i) & 1) == 1
    private def left(bits: Int, num: Long = 1L) = assuming(bits >= 0 && bits < JLong.SIZE)(num << bits)
  }
  implicit class NumericExtensions[A](val x: A)(implicit n: Numeric[A]) {
    import Numeric.Implicits._
    def **(i: Int): A = if (i == 0) n.one else {
      val h = x ** (i/2)
      if (i%2 == 0) h * h else h * h * x
    }
    def distance(y: A) = (x - y).abs()
    def nonNegative: Option[A] = when(n.gteq(x, n.zero))(x)
    def whenNegative(f: => A): A = nonNegative getOrElse f   //e.g. students indexOf "Greg" whenNegative Int.MaxValue
  }
  implicit class IntegralExtensions[A](val x: A)(implicit n: Integral[A]) {
    import scala.collection.immutable.NumericRange, Integral.Implicits._
    def mod(y: A): A = x - ((x / y) * y) //(x/y)*y + (x mod y) == x
    def -->(y: A): NumericRange.Inclusive[A] = NumericRange.inclusive(x, y, if (n.lteq(x, y)) n.one else -n.one)
    def ceilDiv(y: A): A = if (mod(y) == n.zero) x/y else n.one + (x/y)
  }
  implicit def toPoint[A](p: (A, A))(implicit n: Numeric[A]) = new java.awt.geom.Point2D.Double(n.toDouble(p._1), n.toDouble(p._2))
  def desc[A: Ordering]: Ordering[A] = asc[A].reverse  //e.g. students.sortBy(_.height)(desc)
  def asc[A](implicit order: Ordering[A]): Ordering[A] = order
  def map[K] = new {
    def to[V](default: => V): Dict[K, V] = using(_ => default)
    def using[V](f: K => V): Dict[K, V] = new mutable.HashMap[K, V]() {
      override def apply(key: K) = getOrElseUpdate(key, f(key))
    }
  }
  def newMultiMap[K, V] = map[K] to mutable.Set.empty[V]
  def memoize[A, B](f: A => B): A ==> B = map[A] using f
  implicit class FuzzyDouble(val x: Double) extends AnyVal {
    def  >~(y: Double) = x > y + eps
    def >=~(y: Double) = x >= y + eps
    def  ~<(y: Double) = y >=~ x
    def ~=<(y: Double) = y >~ x
    def  ~=(y: Double) = (x distance y) <= eps
  }
  def toPolygon(points: Traversable[(Int, Int)]): java.awt.Polygon = {
    val (xs, ys) = points.unzip
    new java.awt.Polygon(xs.toArray, ys.toArray, points.size)
  }
  def toShape(points: Traversable[(Double, Double)]): java.awt.geom.GeneralPath = {
    val shape = new java.awt.geom.GeneralPath()
    points.headOption foreach {case (x, y) => shape.moveTo(x, y)}
    points.tail foreach {case (x, y) => shape.lineTo(x, y)}
    shape.closePath()
    shape
  }
  def until(until: Int): Range = 0 until until
  def not[A](f: A => Boolean): A => Boolean = {x: A => !f(x)}
  def assuming[A](cond: => Boolean)(f: => A): A = {require(cond); f}
  @inline def when[A](check: Boolean)(f: => A): Option[A] = if (check) f.some else None
  def repeat[U](n: Int)(f: => U): Unit = (1 to n).foreach(_ => f)
  type of[C[_], A] = scala.collection.generic.CanBuild[A, C[A]]
  type ==>[A, B] = collection.Map[A, B]
  val mod: Int = (1e9 + 7).toInt
  val eps: Double = 1e-9
}
/***********************************[Scala I/O]*********************************************/
import Utils._, java.io._, java.util.StringTokenizer

class IO(in: BufferedReader, out: BufferedWriter) extends Iterator[String] with AutoCloseable with Flushable {
  def this(reader: Reader, writer: Writer) = this(new BufferedReader(reader), new BufferedWriter(writer))
  def this(in: InputStream, out: OutputStream) = this(new InputStreamReader(in), new OutputStreamWriter(out))

  private[this] val tokenizers = Iterator.continually(in.readLine()).takeWhile(_ != null).map(new StringTokenizer(_)).buffered
  val printer = new PrintWriter(out, true)

  @inline private[this] def tokenizer() = {
    while(tokenizers.nonEmpty && !tokenizers.head.hasMoreTokens) tokenizers.next()
    when(tokenizers.nonEmpty)(tokenizers.head)
  }

  def read[A](implicit read: IO.Read[A]): A = read.apply(this)
  def read[C[_], A: IO.Read](n: Int)(implicit b: C of A): C[A] = Iterator.fill(n)(read).to[C]

  def readTill(delim: String): String = tokenizer().get.nextToken(delim)
  def readTillEndOfLine(): String = readTill("\n\r")

  def readAll[A: IO.Read]: (Int, Vector[A]) = {
    val data = read[Vector[A]]
    (data.length, data)
  }

  override def next() = tokenizer().get.nextToken()
  override def hasNext = tokenizer().nonEmpty

  def write(obj: Any): this.type = {
    printer.print(obj)
    this
  }
  def writeLine(): this.type = {
    printer.println()
    this
  }
  def writeLine(obj: Any): this.type = {
    printer.println(obj)
    this
  }
  def writeAll(obj: Traversable[Any], separator: String = " "): this.type = write(obj mkString separator)
  def query[A: IO.Read](question: Any): A = writeLine(question).read

  override def flush() = printer.flush()
  def close() = {
    flush()
    in.close()
    printer.close()
  }
}
object IO {
  class Read[A](val apply: IO => A) {
    def map[B](f: A => B): Read[B] = new Read(apply andThen f)
  }
  object Read {
    implicit def collection[C[_], A: Read](implicit b: C of A): Read[C[A]]         = new Read(r => r.read[C, A](r.read[Int]))
    implicit val string                                       : Read[String]       = new Read(_.next())
    implicit val char                                         : Read[Char]         = string.map(_.toTraversable.onlyElement)
    implicit val int                                          : Read[Int]          = string.map(_.toInt)
    implicit val long                                         : Read[Long]         = string.map(_.toLong)
    implicit val bigInt                                       : Read[BigInt]       = string.map(BigInt(_))
    implicit val double                                       : Read[Double]       = string.map(_.toDouble)
    implicit val bigDecimal                                   : Read[BigDecimal]   = string.map(BigDecimal(_))
    implicit def tuple2[A: Read, B: Read]                     : Read[(A, B)]       = new Read(r => (r.read[A], r.read[B]))
    implicit def tuple3[A: Read, B: Read, C: Read]            : Read[(A, B, C)]    = new Read(r => (r.read[A], r.read[B], r.read[C]))
    implicit def tuple4[A: Read, B: Read, C: Read, D: Read]   : Read[(A, B, C, D)] = new Read(r => (r.read[A], r.read[B], r.read[C], r.read[D]))
    implicit val boolean                                      : Read[Boolean]      = string map {s =>
      s.toLowerCase match {
        case "yes" | "true" | "1" => true
        case "no" | "false" | "0" => false
        case _ => s.toBoolean
      }
    }
  }
}

/**
  * Created by ruslan on 3/29/17.
  */
object ProblemA extends App {
    import java.io.{BufferedReader, IOException, InputStreamReader, PrintWriter}
import java.util.StringTokenizer

import scala.collection.mutable
import scala.util.Random
  val in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)))
  val out = new PrintWriter(System.out)

class  FastScanner(val in: BufferedReader) {
  var st: StringTokenizer = _;

  def nextToken(): String = {
    while (st == null || !st.hasMoreTokens()) {
        st = new StringTokenizer(in.readLine);
    }
    return st.nextToken();
  }

  def nextInt(): Integer = {
    Integer.parseInt(nextToken());
  }

  def nextLong(): Long = {
    nextToken().toLong;
  }

  def nextDouble(): Double = {
    nextToken().toDouble;
  }
}

  val startTime = System.currentTimeMillis();

  val n = in.nextInt();
  val a = new Array[Int](n)
  for (i <- 0 until n) a(i) = in.nextInt()

  var sums0 = new Array[(Long, Int)](n)
  var sums1 = new Array[(Long, Int)](n)

  sums0(0) = (0, 0)
  sums1(0) = (0, 0)

  for (i <- 1 until n) {
    val delta = Math.abs(a(i) - a(i - 1));
    sums0(i) = (sums0(i - 1)._1 + delta * (if (i % 2 == 0) -1 else 1), i)
    sums1(i) = (sums1(i - 1)._1 + delta * (if (i % 2 == 1) -1 else 1), i)
  }

  var res = Long.MinValue

  sums0 = sums0.sortBy(_._1)
  sums1 = sums1.sortBy(_._1)

/*  println(sums0.mkString(", "))
  println(sums1.mkString(", "))*/

  def findMin(a: Array[(Long, Int)], index: Int): Long = {
    var res = 0;
    while (res < n && a(res)._2 >= index) res += 1;
    if (res < n) a(res)._1
    else Long.MaxValue
  }

  for(i <- n - 1 to 1 by -1) {
    val del1 = sums0(i)._1 - findMin(sums0, sums0(i)._2)
    val del2 = sums1(i)._1 - findMin(sums1, sums0(i)._2)
    if (del1 > res) res = del1
    if (del2 > res) res = del2
  }

  println(res)

}

/**
  * Created by ruslan on 3/29/17.
  */
object ProblemA extends App {
    import java.io.{BufferedReader, IOException, InputStreamReader, PrintWriter}
import java.util.StringTokenizer

import scala.collection.mutable
import scala.util.Random
  val in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)))
  val out = new PrintWriter(System.out)

class  FastScanner(val in: BufferedReader) {
  var st: StringTokenizer = _;

  def nextToken(): String = {
    while (st == null || !st.hasMoreTokens()) {
        st = new StringTokenizer(in.readLine);
    }
    return st.nextToken();
  }

  def nextInt(): Integer = {
    Integer.parseInt(nextToken());
  }

  def nextLong(): Long = {
    nextToken().toLong;
  }

  def nextDouble(): Double = {
    nextToken().toDouble;
  }
}

  val startTime = System.currentTimeMillis();

  val n = in.nextInt();
  val a = new Array[Int](n)
  for (i <- 0 until n) a(i) = in.nextInt()

  val sums0 = new Array[(Long, Int)](n)
  val sums1 = new Array[(Long, Int)](n)

  sums0(0) = (0, 0)
  sums1(0) = (0, 0)

  for (i <- 1 until n) {
    val delta = Math.abs(a(i) - a(i - 1));
    sums0(i) = (sums0(i - 1)._1 + delta * (if (i % 2 == 0) -1 else 1), i)
    sums1(i) = (sums1(i - 1)._1 + delta * (if (i % 2 == 1) -1 else 1), i)
  }

  var res = Long.MinValue

  sums0.sortBy(_._1)
  sums1.sortBy(_._1)

  def findMin(a: Array[(Long, Int)], index: Int): Long = {
    var res = 0;
    while (res < n && a(res)._2 >= index) res += 1;
    if (res < n) a(res)._1
    else Long.MaxValue
  }

  for(i <- n - 1 to 0 by -1) {
    val del1 = sums0(i)._1 - findMin(sums0, sums0(i)._2)
    val del2 = sums1(i)._1 - findMin(sums1, sums0(i)._2)
    if (del1 > res) res = del1
    if (del2 > res) res = del2
  }

  println(res)

}

/**
  * Created by ruslan on 3/29/17.
  */
object ProblemA extends App {
    import java.io.{BufferedReader, IOException, InputStreamReader, PrintWriter}
import java.util.StringTokenizer

import scala.collection.mutable
import scala.util.Random
  val in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)))
  val out = new PrintWriter(System.out)

class  FastScanner(val in: BufferedReader) {
  var st: StringTokenizer = _;

  def nextToken(): String = {
    while (st == null || !st.hasMoreTokens()) {
        st = new StringTokenizer(in.readLine);
    }
    return st.nextToken();
  }

  def nextInt(): Integer = {
    Integer.parseInt(nextToken());
  }

  def nextLong(): Long = {
    nextToken().toLong;
  }

  def nextDouble(): Double = {
    nextToken().toDouble;
  }
}

  val startTime = System.currentTimeMillis();

  val n = in.nextInt();
  val a = new Array[Int](n)
  for (i <- 0 until n) a(i) = in.nextInt()

  var sums0 = new Array[(Long, Int)](n)

  sums0(0) = (0, 0)

  for (i <- 1 until n) {
    val delta = Math.abs(a(i) - a(i - 1));
    sums0(i) = (sums0(i - 1)._1 + delta * (if (i % 2 == 0) -1 else 1), i)
  }

  var res = Long.MinValue

  sums0 = sums0.sortWith(_._1 < _._1)

  def findMin(a: Array[(Long, Int)], index: Int): Long = {
    var res = 0;
    while (res < n && a(res)._2 >= index) res += 1;
    if (res < n) a(res)._1
    else Long.MaxValue
  }

  for(i <- n - 1 to 0 by -1) {
    val del1 = sums0(i)._1 - findMin(sums0, sums0(i)._2)
    if (del1 > res) res = del1
  }

  println(res)

}

/**
  * Created by ruslan on 3/29/17.
  */
object ProblemA extends App {
    import java.io.{BufferedReader, IOException, InputStreamReader, PrintWriter}
import java.util.StringTokenizer

import scala.collection.mutable
import scala.util.Random
  val in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)))
  val out = new PrintWriter(System.out)

class  FastScanner(val in: BufferedReader) {
  var st: StringTokenizer = _;

  def nextToken(): String = {
    while (st == null || !st.hasMoreTokens()) {
        st = new StringTokenizer(in.readLine);
    }
    return st.nextToken();
  }

  def nextInt(): Integer = {
    Integer.parseInt(nextToken());
  }

  def nextLong(): Long = {
    nextToken().toLong;
  }

  def nextDouble(): Double = {
    nextToken().toDouble;
  }
}

  val startTime = System.currentTimeMillis();

  val n = in.nextInt();
  val a = new Array[Int](n)
  for (i <- 0 until n) a(i) = in.nextInt()

  var sums0 = new Array[(Long, Int)](n)
  var sums1 = new Array[(Long, Int)](n)

  sums0(0) = (0, 0)
  sums1(0) = (0, 0)

  for (i <- 1 until n) {
    val delta = Math.abs(a(i) - a(i - 1));
    sums0(i) = (sums0(i - 1)._1 + delta * (if (i % 2 == 0) -1 else 1), i)
    sums1(i) = (sums1(i - 1)._1 + delta * (if (i % 2 == 1) -1 else 1), i)
  }

  var res = Long.MinValue

  sums0 = sums0.sortBy(_._1)
  sums1 = sums1.sortBy(_._1)

/*  println(sums0.mkString(", "))
  println(sums1.mkString(", "))*/

  def findMin(a: Array[(Long, Int)], index: Int): Long = {
    var res = 0;
    while (res < n && a(res)._2 >= index) res += 1;
    if (res < n) a(res)._1
    else Long.MaxValue
  }

  for(i <- n - 1 to 0 by -1) {
    val del1 = sums0(i)._1 - findMin(sums0, sums0(i)._2)
    val del2 = sums1(i)._1 - findMin(sums1, sums0(i)._2)
    if (del1 > res) res = del1
    if (del2 > res) res = del2
  }

  println(res)

}


object Main {
  def main(args: Array[String]): Unit = {
    val s = new Main()
    s.solve()
    s.out.flush()
  }
}

class Main {
  import java.io._
  import java.util.StringTokenizer

  import scala.collection.mutable
  import scala.util.Sorting
  import math.{abs, max, min}
  import mutable.{ArrayBuffer, ListBuffer}
  import scala.reflect.ClassTag

  val MOD = 1000000007
  val out = new PrintWriter(System.out)

  case class BS(i: Int, rank: Int, cap: Int)

  def solve(): Unit = {
    import java.util
    val N = ni()
    val S = map(N)(_ => ns())

    def read(s: String, i: Int): BS = {
      var rank = 0
      var cap = 0
      REP(s.length) { i =>
        if (s(i) == '(') {
          rank += 1
        } else {
          rank -= 1
        }
        cap = min(cap, rank)
      }

      BS(i, rank, cap)
    }

    val L = S.zipWithIndex.map((read _).tupled).filter(_.cap >= 0) // capが少ないとrankも少ない
    val R = mutable.Map[Int, util.TreeMap[Integer, mutable.Queue[Int]]]() // rank => cap => [id]
    S.zipWithIndex.map((read _).tupled) foreach { r0 =>
      if (r0.rank <= 0) {
        val r = BS(r0.i, -r0.rank, -r0.cap)
        if (!R.contains(r.rank)) R(r.rank) = new util.TreeMap()
        if (!R(r.rank).containsKey(r.cap)) R(r.rank).put(r.cap, mutable.Queue())
        R(r.rank).get(r.cap) += r.i
      }
    }

    val used = Array.ofDim[Boolean](N)

    // L == Rになっちゃだめ
    def selectR(ids: mutable.Queue[Int], l: Int): Option[Int] = {
      val id1 = ids.dequeue()
      if (id1 == l) {
        if (ids.nonEmpty) {
          val selected = ids.dequeue()
          ids += id1
          Some(selected)
        } else {
          None
        }
      } else {
        Some(id1)
      }
    }

    var ans = 0
    L.foreach { l =>
      if (!used(l.i)) {
        if (R.contains(l.rank)) {
          val byCaps = R(l.rank)
          val capR = byCaps.lowerKey(l.rank + 1) // cap <= rank なので <で比較するときは+1しないといけない
          if (capR != null) {
            val rs = byCaps.get(capR)
            selectR(rs, l.i) match {
              case None =>
              case Some(selected) =>
                // ここでfalseになるはずはないんだけど
                if (!used(selected)) {
                  ans += 1
                  if (rs.isEmpty) byCaps.remove(capR)
                  // Rからremoveするのはコスト高いのでやらない
                  used(l.i) = true
                  used(selected) = true
                }
            }
          }
        }
      }
    }

    out.println(ans)
  }

  class InputReader(val stream: InputStream) {
    private val reader = new BufferedReader(new InputStreamReader(stream), 32768)
    private var tokenizer: StringTokenizer = _

    def next(): String = {
      while (tokenizer == null || !tokenizer.hasMoreTokens)
        tokenizer = new StringTokenizer(reader.readLine)
      tokenizer.nextToken
    }

    def nextInt(): Int = next().toInt
    def nextLong(): Long = next().toLong
    def nextChar(): Char = next().charAt(0)
  }
  val sc = new InputReader(System.in)
  def ni(): Int = sc.nextInt()
  def nl(): Long = sc.nextLong()
  def nc(): Char = sc.nextChar()
  def ns(): String = sc.next()
  def ns(n: Int): Array[Char] = ns().toCharArray
  def na(n: Int, offset: Int = 0): Array[Int] = map(n)(_ => ni() + offset)
  def na2(n: Int, offset: Int = 0): (Array[Int], Array[Int]) = {
    val A1, A2 = Array.ofDim[Int](n)
    REP(n) { i =>
      A1(i) = ni() + offset
      A2(i) = ni() + offset
    }
    (A1, A2)
  }
  def nm(n: Int, m: Int): Array[Array[Int]] = {
    val A = Array.ofDim[Int](n, m)
    REP(n) { i =>
      REP(m) { j =>
        A(i)(j) = ni()
      }
    }
    A
  }
  def nal(n: Int): Array[Long] = map(n)(_ => nl())
  def nm_c(n: Int, m: Int): Array[Array[Char]] = map(n) (_ => ns(m))
  def REP(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = offset
    val N = n + offset
    while(i < N) { f(i); i += 1 }
  }
  def REP_r(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = n - 1 + offset
    while(i >= offset) { f(i); i -= 1 }
  }

  def map[@specialized A: ClassTag](n: Int, offset: Int = 0)(f: Int => A): Array[A] = {
    val res = Array.ofDim[A](n)
    REP(n)(i => res(i) = f(i + offset))
    res
  }

  def sumL(as: Array[Int]): Long = {
    var s = 0L
    REP(as.length)(i => s += as(i))
    s
  }

  def cumSum(as: Array[Int]) = {
    val cum = Array.ofDim[Int](as.length + 1)
    REP(as.length) { i =>
      cum(i + 1) = cum(i) + as(i)
    }
    cum
  }
}

import scala.collection.mutable

object C extends App {

  @inline def tokenizeLine = new java.util.StringTokenizer(scala.io.StdIn.readLine)
  def readInts(n: Int) = { val tl = tokenizeLine; Array.fill(n)(tl.nextToken.toInt) }
  def readLongs(n: Int) = { val tl = tokenizeLine; Array.fill(n)(tl.nextToken.toLong) }
  def readBigs(n: Int) = { val tl = tokenizeLine; Array.fill(n)(BigInt(tl.nextToken)) }

  val Array(n) = readInts(1)
  val bs = Array.fill(n){ readLine }

  def eval(b: String, sign: Int): Int = {
    var cur = 0
    var close = 0
    for (c <- b) {
      c match {
        case '(' => cur += sign
        case ')' => cur -= sign
      }
      if (cur > close) close = cur
    }
    close
  }

  val (left, right) = bs.map(b => (eval(b, -1), eval(b.reverse, 1))).partition(_._2 == 0)
  val rightCounts = mutable.Map.empty ++ (right.groupBy(identity).map {
    case (k, v) => k -> v.length
  })

  val z = (0, 0)
  var res = left.count(_ == z) / 2
  for ((l, _) <- left) {
    val rr = (0, l)
    if (rightCounts.getOrElse(rr, 0) > 0) {
      rightCounts(rr) -= 1
      res += 1
    }
  }

  println(res)
}


import java.io._
import java.util.StringTokenizer

import scala.collection.mutable.ListBuffer
import scala.reflect.ClassTag

object Main {
  def main(args: Array[String]): Unit = {
    try {
      val (in, out) =
        if (isOnlineJudge) {
          (
            new FastScanner(new InputStreamReader(System.in)),
            new PrintWriter(System.out)
          )
        } else {
          (
            new FastScanner(new FileReader(new File("src/resource/problem.in"))),
            new PrintWriter(new File("src/resource/problem.out"))
          )
        }
      new DivD(in, out).solve()
      out.flush()
      out.close()
    } catch {
      case e: IOException => e.printStackTrace()
    }
  }

  private[this] val isOnlineJudge = true

  class FastScanner(val streamReader: InputStreamReader) {
    private[this] val reader = new BufferedReader(streamReader, 32768)
    private[this] var tokenizer: StringTokenizer = _

    @inline private[this] final def next(): String = {
      while (tokenizer == null || !tokenizer.hasMoreTokens)
        tokenizer = new StringTokenizer(reader.readLine)
      tokenizer.nextToken
    }

    def nextInt(): Int = Integer.parseInt(next())

    def nextLong(): Long = java.lang.Long.parseLong(next())

    def nextChar(): Char = next().charAt(0)

    def ni(): Int = nextInt()

    def nl(): Long = nextLong()

    def nc(): Char = nextChar()

    def ns(): String = next()

    def ns(n: Int): Array[Char] = ns().toCharArray

    def na(n: Int, offset: Int = 0): Array[Int] = map(n)(_ => ni() + offset)

    def na2(n: Int, offset: Int = 0): (Array[Int], Array[Int]) = {
      val A1, A2 = Array.ofDim[Int](n)
      REP(n) { i =>
        A1(i) = ni() + offset
        A2(i) = ni() + offset
      }
      (A1, A2)
    }

    def nm(n: Int, m: Int): Array[Array[Int]] = {
      val A = Array.ofDim[Int](n, m)
      REP(n) { i =>
        REP(m) { j =>
          A(i)(j) = ni()
        }
      }
      A
    }

    def nal(n: Int): Array[Long] = map(n)(_ => nl())

    def nm_c(n: Int, m: Int): Array[Array[Char]] = map(n)(_ => ns(m))
  }

  def REP(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = offset
    val N = n + offset
    while (i < N) {
      f(i);
      i += 1
    }
  }

  def REP_r(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = n - 1 + offset
    while (i >= offset) {
      f(i);
      i -= 1
    }
  }

  def TO(from: Int, to: Int)(f: Int => Unit): Unit = {
    REP(to - from + 1, from)(f)
  }

  def map[@specialized A: ClassTag](n: Int, offset: Int = 0)(f: Int => A): Array[A] = {
    val res = Array.ofDim[A](n)
    REP(n)(i => res(i) = f(i + offset))
    res
  }

  def sumL(as: Array[Int]): Long = {
    var s = 0L
    REP(as.length)(i => s += as(i))
    s
  }

  def cumSum(as: Array[Int]): Array[Long] = {
    val cum = Array.ofDim[Long](as.length + 1)
    REP(as.length) { i =>
      cum(i + 1) = cum(i) + as(i)
    }
    cum
  }
}

class DivD(fScanner: Main.FastScanner, out: java.io.PrintWriter) {

  import Main._
  import fScanner._

  def solve(): Unit = {
    val n = ni()
    val adj = Array.fill[ListBuffer[Int]](n + 1)(new ListBuffer[Int])
    REP(n-1) { _ =>
      val x = ni()
      val y = ni()

      adj(x) += y
      adj(y) += x
    }

    var toRun = true
    var z = -1
    while (toRun) {
      var x = -1
//      REP(n, 1) { i =>
//        out.println(s"$i  ${adj(i).length}")
//      }
      REP(n, 1) { i =>
        if(adj(i).length == 1) x = i
      }

      var y = -1
      REP(n, 1) { i =>
        if(adj(i).length == 1 && i != x) y = i
      }
      if(x == -1 && y == -1) {
        out.println(s"! $z")
        toRun = false
      } else {
        out.println(s"? $x $y")
        out.flush()
        z = ni()
        if (z == x || z == y) {
          out.println(s"! $z")
          toRun = false
        } else {
          for (i <- adj(x)) {
            adj(i) = adj(i).filter(p => p != x)
          }
          adj(x) = new ListBuffer[Int]
          for (i <- adj(y)) {
            adj(i) = adj(i).filter(p => p != y)
          }
          adj(y) = new ListBuffer[Int]
        }
      }
    }
  }
}

import collection.mutable.HashMap
import collection.mutable.HashSet
object Main {
  def main(args: Array[String]): Unit = {
    val n = readInt
    val d = HashMap[Int, HashSet[Int]]()
    for(i <- 0 until n) d(i + 1) = HashSet[Int]()
    for(_ <- 0 until n - 1) {
      val Array(x, y) = readLine.split(" ").map(_.toInt)
      d(x) += y
      d(y) += x
    }
    var flag = true
    while (d.keySet.size != 1 && flag) {
      val (x, y) = getV(d)
      println(s"? ${x} ${y}")
      System.out.flush

      val v = readInt
      if (v == x) {
        println(s"! $x")
        System.out.flush
        flag = false
      }
      else if (v == y) {
        println(s"! $y")
        System.out.flush
        flag = false
      }
      else {
        removeV(d, x)
        removeV(d, y)
      }
    }
    if (flag) {
      println(s"! ${d.keySet.head}")
      System.out.flush
    }
  }

  def getV(d: HashMap[Int, HashSet[Int]]): (Int, Int) = d.filter{
    case (i, s) => s.size == 1
  }.keys.take(2).toList match {
    case x :: y :: _ => (x, y)
    case _ => ???
  }

  def removeV(d: HashMap[Int, HashSet[Int]], i: Int): Unit = {
    d(d(i).head) -= i
    d -= i
  }
}

import java.io._
import java.util.StringTokenizer

import scala.collection.mutable.ListBuffer
import scala.reflect.ClassTag

object Main {
  def main(args: Array[String]): Unit = {
    try {
      val (in, out) =
        if (isOnlineJudge) {
          (
            new FastScanner(new InputStreamReader(System.in)),
            new PrintWriter(System.out)
          )
        } else {
          (
            new FastScanner(new FileReader(new File("src/resource/problem.in"))),
            new PrintWriter(new File("src/resource/problem.out"))
          )
        }
      new DivD(in, out).solve()
      out.flush()
      out.close()
    } catch {
      case e: IOException => e.printStackTrace()
    }
  }

  private[this] val isOnlineJudge = true

  class FastScanner(val streamReader: InputStreamReader) {
    private[this] val reader = new BufferedReader(streamReader, 32768)
    private[this] var tokenizer: StringTokenizer = _

    @inline private[this] final def next(): String = {
      while (tokenizer == null || !tokenizer.hasMoreTokens)
        tokenizer = new StringTokenizer(reader.readLine)
      tokenizer.nextToken
    }

    def nextInt(): Int = Integer.parseInt(next())

    def nextLong(): Long = java.lang.Long.parseLong(next())

    def nextChar(): Char = next().charAt(0)

    def ni(): Int = nextInt()

    def nl(): Long = nextLong()

    def nc(): Char = nextChar()

    def ns(): String = next()

    def ns(n: Int): Array[Char] = ns().toCharArray

    def na(n: Int, offset: Int = 0): Array[Int] = map(n)(_ => ni() + offset)

    def na2(n: Int, offset: Int = 0): (Array[Int], Array[Int]) = {
      val A1, A2 = Array.ofDim[Int](n)
      REP(n) { i =>
        A1(i) = ni() + offset
        A2(i) = ni() + offset
      }
      (A1, A2)
    }

    def nm(n: Int, m: Int): Array[Array[Int]] = {
      val A = Array.ofDim[Int](n, m)
      REP(n) { i =>
        REP(m) { j =>
          A(i)(j) = ni()
        }
      }
      A
    }

    def nal(n: Int): Array[Long] = map(n)(_ => nl())

    def nm_c(n: Int, m: Int): Array[Array[Char]] = map(n)(_ => ns(m))
  }

  def REP(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = offset
    val N = n + offset
    while (i < N) {
      f(i);
      i += 1
    }
  }

  def REP_r(n: Int, offset: Int = 0)(f: Int => Unit): Unit = {
    var i = n - 1 + offset
    while (i >= offset) {
      f(i);
      i -= 1
    }
  }

  def TO(from: Int, to: Int)(f: Int => Unit): Unit = {
    REP(to - from + 1, from)(f)
  }

  def map[@specialized A: ClassTag](n: Int, offset: Int = 0)(f: Int => A): Array[A] = {
    val res = Array.ofDim[A](n)
    REP(n)(i => res(i) = f(i + offset))
    res
  }

  def sumL(as: Array[Int]): Long = {
    var s = 0L
    REP(as.length)(i => s += as(i))
    s
  }

  def cumSum(as: Array[Int]): Array[Long] = {
    val cum = Array.ofDim[Long](as.length + 1)
    REP(as.length) { i =>
      cum(i + 1) = cum(i) + as(i)
    }
    cum
  }
}

class DivD(fScanner: Main.FastScanner, out: java.io.PrintWriter) {

  import Main._
  import fScanner._

  def solve(): Unit = {
    val n = ni()
    val adj = Array.fill[ListBuffer[Int]](n + 1)(new ListBuffer[Int])
    REP(n-1) { _ =>
      val x = ni()
      val y = ni()

      adj(x) += y
      adj(y) += x
    }

    var toRun = true
    while (toRun) {
      var x = -1
      REP(n, 1) { i =>
        if(adj(i).length == 1) x = i
      }

      var y = -1
      REP(n, 1) { i =>
        if(adj(i).length == 1 && i != x) y = i
      }
      out.println(s"? $x $y")
      out.flush()
      val z = ni()
      if(z == x || z == y) {
        out.println(s"! $z")
        toRun = false
      } else {
        for(i <- adj(x)) {
          adj(i) = adj(i).filter(p => p != x)
        }
        adj(x) = new ListBuffer[Int]
        for(i <- adj(y)) {
          adj(i) = adj(i).filter(p => p != y)
        }
        adj(y) = new ListBuffer[Int]
      }
    }
  }
}

import collection.mutable.HashMap
import collection.mutable.HashSet
object Main {
  def main(args: Array[String]): Unit = {
    val n = readInt
    val d = HashMap[Int, HashSet[Int]]()
    for(i <- 0 until n) d(i + 1) = HashSet[Int]()
    for(_ <- 0 until n - 1) {
      val Array(x, y) = readLine.split(" ").map(_.toInt)
      d(x) += y
      d(y) += x
    }
    while (d.keySet.size != 1) {
      val li = getV(d)
      println(s"? ${li.head} ${li.last}")
      System.out.flush

      val v = readInt
      for(i <- li) {
        if (i != v)
        removeV(d, i, v)
      }
    }
    println(s"! ${d.keySet.head}")
    System.out.flush
  }

  def getV(d: HashMap[Int, HashSet[Int]]): List[Int] = d.map{
    case (i, s) => (i, s.find((j) => d(j).size > 1))
  }.find{
    case (i, Some(j)) => true
    case (_, _) => false
  }.get match {
    case (i, jo) => List(i, jo.get, d(jo.get).find(_ != i).get)
  }
  def removeV(d: HashMap[Int, HashSet[Int]], i: Int, v: Int): Unit = {
    if (d.contains(i)) {
    d(i).foreach((j) => if (j != v) {
      removeV(d, j, i)
    })
    d -= i
  }
  d(v) -= i

  }
}