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)

//abc116_c.cpp
//Sat Feb  2 17:17:35 2019

#include <iostream>
#include <string>
#include <queue>
#include <unordered_map>
#include <vector>
#include <algorithm>
#include <math.h>
#include <set>
#define INTINF 2147483647
#define LLINF 9223372036854775807
using namespace std;
using ll=long long;
typedef pair<int,int> P;

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

	int ans = 0;
	while (1){
		int start = -1;
		int end = -1;
		int flag = 0;
		for (int i=0;i<n;i++){
			if (a[i] > 0){
				start = i;
				flag = 1;
				break;
			}
		}

		if (start == n-1){
			end = n;
		}else {
			for (int i=start+1;i<n;i++){
				if (a[i] == 0){
					end = i;
					break;
				}else if (i==n-1){
					end = n;
				}
			}
		}

		if (start == -1 || end == -1){
			break;
		}

//		cout << start << " " << end << endl;

		for (int i=start;i<end;i++){
			a[i]--;
		}
		ans++;
	}

	cout << ans << endl;
}