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>
#include<algorithm>
using namespace std;

int main(){
	int N;
  	cin >> N;
  	vector<int> h(N);
  	for(int i = 0; i < N ; ++i) cin >> h[i];
  	
  	//高さが全部０になるまでやる。
  	int res = 0;
  	while(true){
    	//最高高さが０だったらおしまい。
      	if(*max_element(h.begin(),h.end())==0)break;
      	
      	//区間分割する
      	int i = 0;
      	while(i<N){
        	if(h[i] == 0) ++i;//0なら何もせずに進む
          	else{
            	++res;//区間の始まり
              	while(i<N&&h[i]>0){
                	--h[i];
                	++i;
                }
            }
        }
    }
	cout << res << endl;
}