import java.util.*;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int p = sc.nextInt();
		int before = 0;
		long dai = 0;
		for (int i = 0; i < p; i++) {
			int height = sc.nextInt();
			if(before > height) {
				dai+=before - height;
			}else {
				before = height;
			}
		}
		System.out.println(dai);
	}
}
/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