import java.util.*;
class Main{
	public static void main(String[] args){
	  Scanner scan = new Scanner(System.in);
	  int N  = scan.nextInt();
      int A = 0;
      long count = 0;
      int max = 0;
      for(int i = 0; i < N; i++){
          A = scan.nextInt();
          if(i == 0)    max = A;
          else{
             if(max <= A) max = A;
          	 count += max - A;
          }
      }
      System.out.println(count);
	}
}
/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