using System;

public class Program

{

    public static void Main()

    {

        var b = new B();

        var bCastedToA = (A) new B();

        b.Write();

        bCastedToA.Write();

        Console.WriteLine();

        b.WriteVirtual();

        bCastedToA.WriteVirtual();

    }

}

​

class A {

    public void Write(){

        Console.WriteLine("a");

    }

    public virtual void WriteVirtual(){

        Console.WriteLine("a");

    }

}

​

class B : A {

    public void Write(){

        Console.WriteLine("b");

    }

    public override void WriteVirtual(){

        Console.WriteLine("overriden b");

    }

}