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: Wrong Answer)

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		Map<Integer,Integer> map = new HashMap<>();

		int min = Integer.MAX_VALUE;
		for (int i = 0; i < N; i++) {
			map.put(i, sc.nextInt());
		}

		int cnt = 0;
		cnt += map.get(0);
		for (int i = 0; i < N; i++) {
			if (i==N-1) {
				break;
			}

			if (map.get(i) <= map.get(i+1)) {
				for (int j = i; j < N-1; j++) {
					if (map.get(j) >= map.get(j+1)) {
						i = j+1;
						continue;
					}
					int num = map.get(j+1) - map.get(j);
					cnt += num;
				}
			}
		}
		System.out.println(cnt);
	}
}