import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

  public static void main(String[] args) throws Exception{
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    int n = Integer.parseInt(br.readLine());
    String[] data = br.readLine().split(" ");
    long[] a = new long[n];
    for(int i = 0; i < n; i++){
      a[i] = Long.parseLong(data[i]);
    }
    long answer = 0;
    long max = a[0];
    for(int i = 1; i < n; i++){
      max = Math.max(max, a[i]);
      answer += Math.abs(max - a[i]);
    }
    System.out.println(answer);
  }
}
/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