import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long tmp1 = 0;
        long tmp2 = 0;
        long ans = 0;

        for (int i = 0; i < n; i++) {
            tmp1 = tmp2;
            tmp2 = sc.nextInt();
            long x = tmp1 - tmp2;
            if (x > 0) {
                ans += x;
                tmp2 += x;
            }
        }
        System.out.println(ans);
    }
}

/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