import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		long[] list = new long[n];
		long max = 0;
		long sum = 0;
		
		for(int i = 0; i < n; i++) {
			list[i] = scan.nextLong();
		}
		
		for(int i = 0; i < n; i++) {
			if(max < list[i]) {
				max = list[i];
			}
			else {
				sum += max - list[i];
			}
		}
		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