
import java.util.*;
public class Main {

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