import java.util.Scanner;
public class Main {
    public static void main(String args[]) {
        Scanner s=new Scanner(System.in);
        int n=s.nextInt();
        long ans=0;
        int prev=s.nextInt();
        for(int i=1;i<n;i++){
            int ele=s.nextInt();
            if(ele<prev){
                ans+=prev-ele;
            }
            else{
                prev=ele;
            }
        }

        System.out.print(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