import java.util.Scanner;

public class Main{

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner sc=new Scanner(System.in);

		int n= sc.nextInt();

		long cnt =0;

		int[] arr= new int[n];

		for(int i =0;i<n;i++) {
			arr[i]=sc.nextInt();
		}

		for(int j=0;j<n-1;j++) {
			if(arr[j+1]<arr[j]) {
				cnt+=arr[j]-arr[j+1];
				arr[j+1]=arr[j];

			}
		}
		System.out.println(cnt);
	}

}

/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