import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();

    long max = sc.nextInt();
    long sum = 0;
    for (int i = 1; i < n; i++) {
      long p = sc.nextInt();
      long step;
      if (max > p) {
        step = max - p;
        sum += step;
      } else {
        max = p;
      }
    }
    System.out.println(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