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