import java.util.*;
import java.io.*;
public class Main {

	public static void main(String[] args) throws java.lang.Exception
    {		
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n =Integer.parseInt(br.readLine()),a[]=new int[n];
		StringTokenizer st=new StringTokenizer(br.readLine());
		for(int i=0; i<n; i++) a[i]=Integer.parseInt(st.nextToken());
		long sum=0;
		for(int i=1; i<n; i++) {
			if(a[i]<a[i-1]) {
				sum+=(a[i-1]-a[i]);
				a[i]=a[i-1];
			}
		}
		System.out.println(sum);
	}

}

/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