import java.util.*;
 
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int num = sc.nextInt();
    int array[] = new int[num];
    for(int i = 0;i < num;i++){
      array[i] = sc.nextInt();
    }
    long count = 0;
    int max = 0;
    for(int i = 0;i < num;i++){
      if(max < array[i]){
        max = array[i];
      }
      if(array[i] < max){
        count += max - array[i];
      }
    }
    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