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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include<iostream>
using namespace std;

int a[101];
int N;

bool water(){
    int s,g;
    s = -1; 
    g = -1;
    for(int i = 0; i < N; i++){
        if((s < 0) && a[i] > 0){
            s = i;  
        }
        if((s >= 0) && (a[i] == 0) && (g < 0)){
            g = i - 1;
            break;
        }
        if(s >= 0 && i == N - 1){
            g = i;
        }
    }
    //cout << "s:" << s << ", g:" << g << endl;
    bool flag = false;
    for(int i = s; i <= g && s >= 0; i++){
        flag = true;
        a[i] -= 1;
    }
    /*
    for(int i = 0; i < N; i++){
        cout << a[i] << ' ';
    }
    cout << endl;
    */
    return flag;
}

int main(){
    cin >> N;
    for(int i = 0; i < N; i++){
        cin >> a[i];
    }
    int ans = 0;
    while(water()){
        ans += 1;
    }
    cout << ans << endl;
}