using System;

public abstract class car

{

    public abstract void wheels();

    public virtual string fuel()

    {

        return "fuel used";

    }

}

public class cardup{

    public virtual string fuelo()

    {

        return "fuel used";

    }

}

public class BMWdup:cardup

{

public override string fuelo()

    {return "bmw fuelused";

    }

}

public class BMW:car

{

    public override void wheels()

    {

    Console.WriteLine("4");

    }

    public override string fuel()

    {

        return "petrol/deisel";

    }

}

public class implement

{

    public string getdet(cardup test)

    {

        return test.fuelo();

    }

}

public class Program

{

    public static void Main()

    {

        implement obj3=new implement();

        BMWdup obj4=new BMWdup();

        string strobj3=obj3.getdet(obj4);

        Console.WriteLine(strobj3);

        cardup obj2=new cardup();

        string ans=obj2.fuelo();

        Console.WriteLine(ans);

        BMW obj1=new BMW();

        obj1.wheels();

        Console.WriteLine("Hello World");

    }

}