import java.util.Scanner;
 
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 sum = 0;
		int i = 0;
 
		for (int j = i + 1; j < n; j++) {
			if (a[i] >= a[j]) {
				sum += a[i] - a[j];
			} else {
				i = j;
			}
		}
		
		
		
		System.out.println(sum);
		sc.close();
	
	}
}
/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