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 Kotlin (1.0.0) (judge verdict: Accepted)

import java.util.*

fun main(args: Array<String>) {
    val sc = Scanner(System.`in`)
  	val N = sc.nextInt()
  	val H = IntArray(N){0}
  	for (i in 0 until N) {
  	    H[i] = sc.nextInt()
    }
    var ans = 0
    val list = mutableListOf(H.toMutableList())
    while (list.size>0) {
        var lis = list.removeAt(0)
        val min = lis.min()!!
        ans += min
        for (i in 0 until lis.size) lis[i] -= min
        while (lis.size > 0) {
            val id = lis.indexOf(0)
            if (id == -1) {
                list.add(lis)
                break
            }
            id is Int
            if (id != 0) {
                list.add(lis.subList(0,id))
            }
            lis = lis.drop(id+1).toMutableList()
        }
    }
    println(ans)
}