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 <stdio.h>
#include <cstring>
#include <cstdio>
#include <math.h>
#include <algorithm>
#include <vector>
#include <string>
#include <stdlib.h>
#include <queue>
#include <stack>
#include <utility>
#include <fstream>
#include <random>
#include <map>
#include <unordered_map>
#include <cstdlib>
#include <functional>
#include <random>
#include <time.h>
#include <chrono>
#include <sstream>
#include <iomanip>
#define rep(i,n) for(int i=0;i<n;i++)
#define rrep(i,n) for(int i=n-1;i>=0;i--)
#define FOR(i,a,b) for(int i=a;i<b;i++)
#define ll long long
#define INF 1000000001
#define mod 1000000007
#define sort(s) sort(s.begin(), s.end());
#define reverse(s) reverse(s.begin(), s.end());
int dx[4] = { 0,1,0,-1 };
int dy[4] = { 1,0,-1,0 };
using namespace std;
int POW(int x, int y) { return int(pow(double(x), double(y))); }
double log(double a, double b) { return log(b) / log(a); }

unsigned int randxor()
{
	static unsigned int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
	unsigned int t;
	t = (x ^ (x << 11)); x = y; y = z; z = w; return(w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}

vector<int> h;
int f(int a, int b) {
	int mi=101;

	FOR(i, a, b) {
		mi = min(mi, h[i]);
	}
	int ans = mi;
	int index = 0;
	FOR(i, a, b) {
		h[i] -= mi;
		if (h[i] == 0) {
			if (index != i) {

				ans += f(index, i);
			}
			index = i + 1;
		}
	}
	if (h[b-1] != 0) {
		ans += f(index, b);
	}
	return ans;
}

int main() {
	int n;
	cin >> n;
	h.resize(n);
	rep(i, n) {
		cin >> h[i];
	}
	cout << f(0, n) << endl;
	return 0;

}