object Main extends App {
  var n = scala.io.StdIn.readInt()
  var s = scala.io.StdIn.readLine()
  var inputArray =  s.split(" ").map(_.toInt)
  var i = 0

  def minusWater(s: Seq[Int]): Seq[Int] = {
    var arrayIndex = Seq.empty[Int]
    val maxIndex = s.indexOf(s.max)
    val b1 = new Breaks
    b1.breakable{
      for(i<-maxIndex to n - 1) {
        if (s(i) == 0) {
          b1.break()
        } else {
          arrayIndex :+= i
        }
      }
    }
    if (maxIndex > 0) {
      val b2 = new Breaks
      b2.breakable{
        for(i<-(maxIndex-1) to 0 by -1) {
          if (s(i) == 0) {
            b2.break()
          } else {
            arrayIndex :+= i
          }
        }
      }
    }

    s.zipWithIndex.map{ h =>
      if (arrayIndex.find(_ == h._2).isDefined) {
        h._1 - 1
      }else {
        h._1
      }
    }
  }

  def judgeSeq(s: Seq[Int]): Unit = {
    i += 1
    val seqAfterWater = minusWater(s)
    if (seqAfterWater.filterNot(_ == 0).isEmpty) {
      println(i)
    } else {
      judgeSeq(seqAfterWater)
    }
  }
  judgeSeq(inputArray)
}