import java.util.*;

public class Main {
    public static void main(String[] args) {
	Scanner sc = new Scanner(System.in);
	int n = sc.nextInt();
	int[] a = new int[n];
	for (int i=0; i<n; i++) a[i] = sc.nextInt();
	int low = a[0];
	long sum = 0;
	for (int i=1; i<n; i++) {
	    if (low <= a[i]) low = a[i];
	    else {
		sum = sum + low - a[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