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 <algorithm>
#include <functional>
#include <string>
#include <vector>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <map>
#include <set>
#include <list>
#include <unordered_set>
#include <unordered_map>
#include <stdlib.h>

using namespace std;
 
typedef long long i64;
typedef pair<i64, i64> P;

template<class T>
const T INF = numeric_limits<T>::max();
template<class T>
const T SINF = numeric_limits<T>::max() / 10;
static const i64 MOD = 1000000007;

//int dx[4] = {0,1,0,-1}, dy[4] = {-1,0,1,0};
//int dx[5] = {-1,0,0,0,1}, dy[5] = {0,-1,0,1,0};
//int dx[8] = {-1,0,1,1,1,0,-1,-1}, dy[8] = {1,1,1,0,-1,-1,-1,0};
//int dx[9] = {-1,0,1,1,1,0,-1,-1,0}, dy[9] = {1,1,1,0,-1,-1,-1,0,0};

struct edge {
	i64 from, to, cost;
	edge(i64 to, i64 cost) : from(-1), to(to), cost(cost) {}
	edge(i64 src, i64 to, i64 cost) : from(src), to(to), cost(cost) {}
};

template<typename T>
vector<T> make_v(size_t a){return vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
	return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

template<typename T,typename V>
typename enable_if<is_class<T>::value==0>::type
fill_v(T &t,const V &v){t=v;}

template<typename T,typename V>
typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t,const V &v){
	for(auto &e:t) fill_v(e,v);
}

//-----end of template-----//

int h[100];

int rec(int l, int r){
	if(r - l <= 1){
		int tmp = h[l];
		h[l] = 0;
		return tmp;
	}
	int idx, m;
	m = 100;
	for(int i = l; i < r; ++i){
		if(m > h[i]){
			m = h[i];
			idx = i;
		}
	}
	int sum = m, z = l;
	for(int i = l; i < r; ++i){
		h[i] -= m;
		if(h[i] == 0){
			sum += rec(z, i);
			z = i + 1;
		}
	}
	sum += rec(z, r);
	return sum;
}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	int n;
	cin >> n;
	for(int i = 0; i < n; ++i){
		cin >> h[i];
	}
	cout << rec(0, n) << endl;
}