package array;

import java.util.Scanner;

public class rainwater {

public static int rain(int arr[], int n) {

int trapwater = 0;

int leftmax[] = new int[n];

leftmax[0] = arr[0];

int rightmax[] = new int[n];

rightmax[n-1] = arr[n-1];

for (int i = 1; i < n; i++) { // leftmax aux array

leftmax[i] = Math.max(arr[i], leftmax[i-1]);

}

for (int a = n-2; a >= 0; a--) { // rightmax aux array

rightmax[a] = Math.max(arr[a], rightmax[a+1]);

}

for (int b = 0; b < n; b++) {

int h = Math.min(rightmax[b], leftmax[b]);

int hw = h - arr[b];

if (hw > 0) {

trapwater += hw;

}

}

return trapwater;

}

public static void main(String args[]) {

Scanner sc = new Scanner(System.in);

System.out.println("Enter the number of elements you want in the array");

int k = sc.nextInt();

int arr[] = new int[k];

System.out.println("Enter the elements you want in the array");

for (int m = 0; m < k; m++) {

arr[m] = sc.nextInt();

}

int trapwater = rain(arr, k);

System.out.println(trapwater);

sc.close();

}

}