using System;

using System.Linq;

​

​

class Test

{

    private int _myInt;

    public int MyInt { get { return _myInt ;}  set {if (value == 666) {Console.WriteLine("Fuck off"); return;} _myInt = value;}}

}

​

public class Program

{

    public static void Main()

    {

        var test = new Test();

        test.MyInt = 666;

    }

}