import java.util.*;

public class Main{
  public static void main(String[] args){
  	Scanner sc = new Scanner(System.in);
    
    int n = sc.nextInt();
    long sum = 0l;
    long high = sc.nextLong();
    for(int i = 1; i < n; i++){
      long next = sc.nextLong();
      if(high > next){
      	sum += (high - next);
      } else {
        high = next;
      }
    }
    
    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