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.Scanner;
import java.util.Stack;

public class Main {

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] k = new int[n];
		for(int i=0;i<n;i++) {
			k[i] = in.nextInt();
		}
		Stack<int[]> stack = new Stack<>();
		int[] start = new int[2];
		start[0] = 0;
		start[1] = n-1;
		stack.push(start);
		int ans = 0;
		while(!stack.isEmpty()) {
			int[] tmp = stack.pop();
			int idx_l = tmp[0];
			int idx_r = tmp[1];
			int min = Integer.MAX_VALUE;
			int min_idx = -1;
			for(int i=idx_l;i<=idx_r;i++) {
				if(k[i]<min) {
					min = k[i];
					min_idx = i;
				}
			}
			ans += min;
			for(int i=idx_l;i<=idx_r;i++) {
				k[i] -= min;
			}
			if(idx_l<=min_idx-1) {
				int[] left = new int[2];
				left[0] = idx_l;
				left[1] = min_idx-1;
				stack.push(left);
			}
			if(min_idx+1<=idx_r) {
				int[] right = new int[2];
				right[0] = min_idx+1;
				right[1] = idx_r;
				stack.push(right);
			}	
		}
		System.out.println(ans);
		in.close();
	}

}