import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {


    public static void main(String[] args) throws IOException {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        int n=Integer.parseInt(br.readLine().trim());
        String[] s=br.readLine().split(" ");
        long[] a=new long[n];
        long res=0;
        for(int i=0;i<n;i++){
            a[i]=Long.parseLong(s[i].trim());
        }

        long last=a[0];
        for(int i=1;i<n;i++){
            if(a[i]<last){
                res+=(last-a[i]);
            }
            last=Math.max(last,a[i]);
        }
        System.out.println(res);





    }






}

/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