import java.util.*;

public class Main {
	public static void main(String[] args){
 
        Scanner sc = null;
        sc = new Scanner(System.in);
        long ans = 0;
        long max = 0;
        long work = 0;
        int n = sc.nextInt();
        for (int i = 0; i < n; i++) {
            work = sc.nextLong();
            if (i != 0 && work < max) {
                ans += (max - work);
            }else if(work > max){
                max = work;
            }
        }
        sc.close();
        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