using System;

​

public class Program

{

    public static void Main(string[] args)

    {

        var a = new A();

        //Your code goes here

        Console.WriteLine(a?.b?.b2 ?? "null it is");

    }

}

​

public class A

{

    public B b

    {

        get;

        set;

    }

}

​

public class B

{

    public B b1

    {

        get;

        set;

    }

​

    public string b2

    {

        get

        {

            return "mads";

        }

    }

}