import java.util.*;

public class Main {
	public static void main(String[] args) {
		
		Scanner keyboard = new Scanner(System.in); 
		
		int N = keyboard.nextInt();
		long a1 = keyboard.nextLong();
		long sum = 0;
		
		for(int n=1; n<N; n++) {
			long a = keyboard.nextLong();
			if(a<a1) {
				sum += a1-a;
			}else {
				a1 = a;
			}
		}
		
		System.out.print(sum);
		keyboard.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