import java.util.*;
import java.lang.*;
import java.math.BigInteger;
public class Main{
  public static void main(String arg[])
  {
   Scanner sc=new Scanner(System.in);
  
  int n=sc.nextInt();
  long t=0;
  int max=0;
  for(int i=0;i<n;i++)
  {
      int x=sc.nextInt();
      max=Math.max(max, x);
      t+=max-x;
  }
      System.out.println(t);
    
  }
}
/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