import java.util.Scanner;

public class Main {
	
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		int  n = sc.nextInt();
		
		long arr[] = new long[n];
		
		for(int i=0; i<n; i++) {
			arr[i] = sc.nextLong();
		}
		
		long total = 0;
		long largest = arr[0];
		for(int i=1; i<n; i++) {
			
			if(arr[i] <= largest) {
				total += largest - arr[i];
			}else if(arr[i] > largest) {
				largest = arr[i];
			}
		}
		
		System.out.println(total);
		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