import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		int N = scan.nextInt();
		int A[] = new int[N];
		long step = 0;
		int max = 0;
		for(int i=0; i<N; i++) {
			A[i] = scan.nextInt();
		}

		max = A[0];
		for(int i=0; i<N; i++) {
			if(max <= A[i]) {
				max = A[i];
			}
			step += max - A[i];
		}
		System.out.println(step);
	}
}

/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