Problem:
Score : 300 points

Problem Statement

In a flower bed, there are N flowers, numbered 1,2,......,N. Initially, the heights of all flowers are 0.
You are given a sequence h=\{h_1,h_2,h_3,......\} as input. You would like to change the height of Flower k to h_k for all k (1 \leq k \leq N), by repeating the following "watering" operation:

Specify integers l and r. Increase the height of Flower x by 1 for all x such that l \leq x \leq r.

Find the minimum number of watering operations required to satisfy the condition.

Constraints

1 \leq N \leq 100

0 \leq h_i \leq 100

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
h_1 h_2 h_3 ...... h_N

Output

Print the minimum number of watering operations required to satisfy the condition.

Sample Input 1

4
1 2 2 1

Sample Output 1

2

The minimum number of watering operations required is 2.
One way to achieve it is:

Perform the operation with (l,r)=(1,3).

Perform the operation with (l,r)=(2,4).

Sample Input 2

5
3 1 2 3 1

Sample Output 2

5

Sample Input 3

8
4 23 75 0 23 96 50 100

Sample Output 3

221

Solution in Scala (2.11.7) (judge verdict: Accepted)

import java.util.Scanner

import scala.annotation.tailrec

object Main extends App {
  val sc = new Scanner(System.in)

  val n = sc.nextInt
  val hl = Seq.fill(n)(sc.nextInt)


  val res = cntLoop(hl)
  println(res)

  @tailrec
  def cntLoop(list: Seq[Int] , cnt: Int = 0): Int = {
    if (list.forall(_ == 0) ) cnt
    else cntLoop(elementMinusOne(list), cnt + separate(list).size)
  }

  @tailrec
  def separate(list: Seq[Int], lists: Seq[Seq[Int]] = Seq.empty): Seq[Seq[Int]] = {
    list match {
      case Nil => lists
      case nonEmpty => {
        val target = nonEmpty.dropWhile(_ == 0)
        val (take, drop) = target.span(_ > 0)
        val next = drop.dropWhile(_ == 0)
        separate(next, lists :+ take)
      }
    }
  }

  def elementMinusOne(list: Seq[Int]): Seq[Int] = {
    list.map{
      case 0 => 0
      case e => e - 1
    }
  }
}