using System.IO;
using System;

abstract class A
{
    public void Testme(A other)
    {
        Console.WriteLine("value from this: " + Value() + " value from other: " + other.Value());
    }
    
    protected abstract string Value();
}

class B : A
{
    protected override string Value()
    {
        return "B class";
    }
}

class C : A
{
    protected override string Value()
    {
        return "C class";
    }
}



class Program
{
    static void Main()
    {
        B b = new B();
        C c = new C();
        
        b.Testme(c);
    }
}

// value from this: B class value from other: C class