import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力(スペース改行関係なし)
		int n = sc.nextInt();
        long soukei = 0;
      	int amae = 0;

      	for(int i = 0 ; i < n ; i++){
        	int a = sc.nextInt();
        	if(a < amae){
            	soukei = soukei + (amae-a);
            }else{
            	amae = a;
            }
        	
        }

		System.out.println(soukei);

		
	}
}
/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