
import java.util.Map.Entry;
import java.util.*;
 
//import org.w3c.dom.css.Counter;
 
public class Main {
//public class App {
 
    public static void main(final String[] args){
     //スキャン
     final Scanner s = new Scanner(System.in);
      //String N = Integer.parseInt(s.next());
      long N = Integer.parseInt(s.next());
      //int T = Integer.parseInt(s.next());
      //int ans = N /X;
      //String hoge = s.next();
      //int huge = hoge.length();
      //int hage = 0;
      int tmp = 0;
      long ans=0;
    for(long i =0;i<N;i++){
        int T = Integer.parseInt(s.next());
        if(tmp >T){
            ans += tmp -T;
        }else{
            tmp = T;
        }
    }
    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