using System;

​

public class Program

{

    public static void Main()

    {

        var a = new A();

        a.M();

        var c = new C();

        c.M();

        ((A)c).M();

    }

}

​

public class C : A

{

    public new void M()

    {

        Console.WriteLine("M");

    }

}

​

public class A

{

    public void M()

    {

        Console.WriteLine("A");

    }

}