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 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <math.h>

int min(int *s, int a, int b){
    int min = 101;
    int num = -1;
    for (int i = a; i<= b; i++){
        if(min > s[i]) {
            num = i;
            min = s[i];
        }
    }
    return num;
}

void func(int s[], int a, int b, int *count){
    int m = min(s, a, b);
    if(m == -1);
    else if(s[m] == 0){
        func(s, a, m-1, count);
        func(s, m+1, b, count);
    }
    else if (a == b){
        *count += s[a];
        s[a] = 0;
    }
    else{
        int m1 = s[m];
        *count += m1;
        for(int i = a; i <= b; i++){
            s[i] -= m1;
        }
        func(s, a, m-1, count);
        func(s, m+1, b, count); 
    }
}

int main(){
    int N;
    scanf("%d",&N);
    int h[N];
    int count = 0;
    for (int i = 0; i< N; i++){
        scanf("%d", &h[i]);
    }
    func(h, 0, N-1, &count);
    printf("%d\n", count);
    return 0;
}