import java.util.Scanner;


public class Main {
	public static void main (String args[]) throws Exception{
		Scanner scan = new Scanner(System.in);
		long n = scan.nextLong();
		long max = scan.nextLong();
		long sum = 0;
		
		for(long i = 0; i < n - 1 ; i++) {
			long a = scan.nextLong();
			if(a < max) {
				sum += max - a;
			} else if(max < a){
				max = a;
			}
		}
		
		System.out.print(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