using System;

class A 

{

    private int q = 11;

    public int Q

    {

        get { return q - 1; }

        set { q = value + 2; }

    }

    public A(int i) { q = i; }

    public int this[int i]

    {

        get { return Q - i; }

        set { Q = value + i; }

    }

}

​

public class Program

{

    public static void Main()

    {

        A a = new A(2);

        a[3] = 5;

        Console.WriteLine("{0}", a.Q);

        Console.WriteLine("{0} {1}", a[3], a[4]);

        a[3] = a[2];

        Console.WriteLine("{0} {1}", a[2], a[3]);

    }

}