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.lang.Math

val MOD: Int = 1000000000 + 7
val MODL: Long = MOD.toLong()

var H = IntArray(1)

fun main(args: Array<String>)
{
    val n = readLine()!!.toInt()
    H = readLine()!!.split(" ").map{it.toInt()}.toIntArray()

    var ans = water(0, n-1)
    println(ans)
}

fun water(from: Int, to: Int): Int {
    var dec = false
    var div = -1
    for (i in from until to) {
        if (H[i] > H[i+1] && !dec) {
            dec = true
            continue
        }
        if (dec && H[i] < H[i+1]) {
            dec = false
            if (div == -1) {
                div = i
            } else {
                div = if (H[i] > H[div]) div else i
            }
        }
    }

    var cnt: Int
    if (div != -1) {
        for (i in from..to) {
            H[i] -= H[div]
            if (H[i] < 0) H[i] = 0
        }
        cnt = H[div] + water(from, div-1) + water(div+1, to)
    } else {
        var n = -1
        for (i in from..to) {
            n = if (H[i] > n) H[i] else n
        }
        cnt = n
    }
    return cnt
}