Q4_1094.java

/*
 * Name: Amaresh Swain
 * Reg No: 2341019646
 * PS LINK: https://cses.fi/problemset/task/1094
 */

import java.util.Scanner;
public class Q4_1094
{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        long arr[]=new long[n];
        for (int i = 0; i < n; i++)
        {
            arr[i]=sc.nextLong();
        }

        long s=0;
        for (int i = 1; i < n; i++) {
            if(arr[i]<arr[i-1])
            {
                s+=arr[i-1]-arr[i];
                arr[i]=arr[i-1];
            }
        }

        System.out.println(s);
    }
}