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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
import static java.lang.Math.*;
import java.math.BigInteger;

public class Main {
    static int cnt = 0;
    
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		// 入力
		int n = sc.nextInt();
		int[] h = new int[n];
		for(int i = 0; i < n; i++){
		    h[i] = sc.nextInt();
		}

		// 計算
		int result = 0;
		dfs(h);
		result = cnt;
		// 出力
		System.out.println(result);
        
	}
	
	static void dfs(int[] a){
	    //System.out.println(Arrays.toString(a));
	    ArrayList<Integer> list = new ArrayList<Integer>();
	    int min = 1000;
	    for(int i = 0; i < a.length; i++){
	        if(a[i] < min) min = a[i];
	    }
	    cnt += min;
	    for(int i = 0; i < a.length; i++){
	        if(a[i] == min) list.add(i);
	    }
	    list.add(a.length);
	    int l = 0;
	    for(int i = 0; i < list.size(); i++){
	        int r = list.get(i);
	        int len = r - l;
	        if(len > 0){
	            int[] next = new int[len];
	            for(int j = l; j < l + len; j++){
	                next[j - l] = a[j] - min;
	            }
	            dfs(next);
	        }
	        l = r + 1;
	    }
	}
}