import java.util.Scanner;

public class Main {
    static Scanner sc = new Scanner(System.in);    
    public static void main(String[] args) {
        int n = sc.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextLong();
        }
        long highest = 0, ans = 0;
        for (long a: arr){
            if (a < highest){
                ans += highest - a;
            }else{
                highest = a;
            }
        } 
        System.out.println(ans);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz