import java.util.*;
public class Main{
  public static void main(String args[]){
  	Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    long arr[]=new long[n];
    for(int i=0;i<n;i++){
    	arr[i]=sc.nextLong();
    }
    int i=0,start=0;
    long count=0;
    while(i<n){
    	if(arr[start]>=arr[i]){
          count+=arr[start]-arr[i];
        }
      else{
      	start=i;
      }
      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