import java.util.Scanner;

public class Main {
	static int N=0;
	static long count=0L;
	static long max=0L;
	public static void main(String args[]) {
		try(Scanner sc = new Scanner(System.in)){
			N = Integer.parseInt(sc.next());
			Long a[] = new Long[N]; 
			for(int i=0;i<N;i++) {
				a[i] = Long.parseLong(sc.next());
			}
			for(int i=0;i<N;i++) {
				if(max<a[i]) {
					max = a[i];
				} else {
					count += max-a[i];
				}
				
			}
		}
		System.out.println(count);
	}
}
/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