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 <bits/stdc++.h>
#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define REPS(i, n) for (int i = 1, i##_len = (n); i < i##_len; ++i)
#define ALL(x) (x).begin(), (x).end()
#define PRINT(A) std::cout << (#A) << ":" << (A) << std::endl;

typedef long long int ll;
const int MOD = 1e9 + 7;
const int INF = 1e9;

using namespace std;

int main() {
  int N;
  cin >> N;
  int h[N + 1];
  REP(i, N) cin >> h[i];
  h[N] = 0;

  bool end = false;
  ll ans = 0;
  while (!end) {
    int min_val = INF;
    int start = 0;
    end = true;
    REP(i, N + 1) {
      if (h[i] > 0) {
        min_val = min(min_val, h[i]);
        end = false;
      }
      if (h[i] == 0) {
        for (int j = start; j < i; j++) {
          h[j] -= min_val;
        }
        if (min_val != INF) {
          ans += min_val;
        }
        start = i + 1;
        min_val = INF;
      }
    }
  }
  cout << ans << endl;
}