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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int[] h = new int[N];
    int count =0;
    for (int i =0; i<N; i++) {
      h[i] = sc.nextInt();
    }
    
    int a =0; int b=0;
    L:while (a<= N-1 && b<= N-1) {
      if (h[a] ==0) {
        a++;
        continue;
      }
      //aを決定
      b = a;
      while (b <= N-1) {
        if (h[b] !=0 && b != N -1) {
          b++;
          continue;
        } else {
          for (int i =a; i<=b; i++) {
            h[i]--;
            if (h[i] <0) {
              h[i] =0;
            }
          }
        }
        count++;
        continue L;
      }
    }
    System.out.println(count);
  }
}