using System;

public class Program

{

    public class test 

    {

        public string Age { get; set; } = "123";

        public test(string age) {

            this.Age = age;

            Console.WriteLine(this.Age);

        }

    }

    public static void Main()

    {

        var a = new test(null);

        Console.WriteLine("Hello World");

    }

}