using System;

​

public class Program

{

    public static void Main()

    {

​

        for(int num = 1000; num < 10000; num++)

        {

            int a = num / 1000;

            int b = (num / 100) % 10;

            int c = (num / 10) % 10;

            int d = num % 10;

            if((b == 2 * a) && (c == 2 * b || d == 2 * c))

            {

             Console.WriteLine(num);

             }

        }

     }

 }