import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] arr = new int[n];
        for(int i=0; i<n; i++)
            arr[i] = in.nextInt();
        int maxSoFar = arr[0];
        long ans = 0;
        for(int i : arr) {
            if(i > maxSoFar) {
                maxSoFar = i;
            } else {
                ans += (long) (maxSoFar - i);
            }
        }
        System.out.println(ans);
        in.close();
    }
}
/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