import java.util.*;
import java.io.*;
public class Main {
    public static void main(String[] args) throws Exception{
        StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        in.nextToken();
        int N = (int) in.nval;
        int[] a = new int[N];
        for(int i = 0; i < N; i++){
            in.nextToken();
            a[i] = (int) in.nval;
        }
        int j = 0;
        double ans = 0;
        for(int i = 1; i < N; i++){
            if(a[i] < a[j]){
                ans += (a[j] - a[i]);
            }else{
                j = i;
            }
        }
        System.out.format("%.0f",ans);
        System.out.println();
    }
}

/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