Main.java

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }
        int[] left = new int[n];
        int[] right = new int[n];
        left[0] = arr[0];
        right[n - 1] = arr[n - 1];
        for (int i = 1; i < n; i++) {
            left[i] = Math.max(arr[i], left[i - 1]);
        }
        for (int i = n - 2; i >= 0; i--) {
            right[i] = Math.max(arr[i], right[i + 1]);
        }
        // for (int i = 0; i < n; i++) {
        //     System.out.print(left[i] + " ");
        // }
        // System.out.println();
        // for (int i = 0; i < n; i++) {
        //     System.out.print(right[i] + " ");
        // }
        // System.out.println();
        int water = 0;
        for (int i = 0; i < n; i++) {
            water += Math.min(left[i], right[i]) - arr[i];
        }
        System.out.print(water);
    }
}