using System;

public class Program

{

    public class Box

    {

        private readonly Box insideBox;

​

        public Box (Box box = null)

        {

            insideBox = box;

        }

​

        public int NumberOfInsideBoxes

        {

            get 

            {

                if (insideBox != null)

                    return 1 + insideBox.NumberOfInsideBoxes;

​

                return 0;

            }

        }

    }

    public static void Main()

    {

        Console.WriteLine(new Box(new Box(new Box())).NumberOfInsideBoxes); // 2

    }

}