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>
#include <vector>

using namespace std;

int solve(vector<int>& h, int l, int r) {
    int min = 100;
    for (int i = l; i < r; i++) {
        if (min > h[i]) {
            min = h[i];
        }
    }

    for (int i = l; i < r; i++) {
        h[i] -= min;
    }

    int cnt = min;
    for (int i = l; i < r; i++) {
        if (h[i] > 0) {
            for (int j = i + 1; j <= r; j++) {
                if (j == r || h[j] == 0) {
                    cnt += solve(h, i, j);
                    i = j - 1;
                    break;
                }
            }
        }
    }

    return cnt;
}

int main() {
    int n;
    cin >> n;

    vector<int> h(n);
    for (int i = 0; i < n; i++) {
        cin >> h[i];
    }

    cout << solve(h, 0, n) << endl;
}