import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int[] a = new int[n];
        for(int i=0; i<n; i++){
            a[i] = sc.nextInt();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    }
}
/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