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>
#include <map>
#include <set>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <random>
#include <chrono>
#include <queue>
using namespace std;
typedef long long ll;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
#define INF 1000000000
#define MOD 1000000007
#define EPS 0.00000001

int main(){
    int N; cin >> N;
    int ans = 0;
    vector<int> H(N);
    for(int &h:H)
        cin >> h;
    
    bool u = true;
    bool d = true;
    for(int i=0; i<N-1; i++){
        
        if(u && H[i]>H[i+1]){
            u = false;
            d = true;
            ans += H[i];
        }
        if(d && H[i]<H[i+1]){
            u = true;
            d = false;
            ans -= H[i];
        }
    }
    if(u) ans+=H[N-1];
    else ans-=H[N-1];

    int yama = 0;
    u = true;
    d = true;
    for(int i=0; i<N-1; i++){
        
        if(u && H[i]>H[i+1]){
            yama++;
            u = false;
            d = true;
        }
        if(d && H[i]<H[i+1]){
            if(yama==0) ans += H[i];
            u = true;
            d = false;
        }
    }

    yama = 0;
    u = true;
    d = true;
    for(int i=N-1; i>0; i--){
        
        if(u && H[i]>H[i-1]){
            yama++;
            u = false;
            d = true;
        }
        if(d && H[i]<H[i-1]){
            if(yama==0) ans += H[i];
            u = true;
            d = false;
        }
    }
    
    
    
    cout << ans << endl;
}