import java.util.Scanner;
public class Main {
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    long[] arr = new long[n];
    long sum = 0;
    for(int i=0;i<n;i++){
      arr[i] = scan.nextLong();
    }
    
    for(int i=1;i<n;i++){
      if(arr[i-1] > arr[i]){
        long d = arr[i-1] - arr[i];
        arr[i] = arr[i] + d;
        sum = sum + d;
      }
    }
    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