using System;

abstract class A{
	int dato;
}

abstract class B : A{
	public abstract void Metodo();
}

class C : B{
	public override void Metodo(){
		Console.WriteLine("yeup");
	}
}

class Test{
	static void Main(){
		A c = new C();
		B b = (B)c;
		b.Metodo();
	}
}