using System;

using System.Collections.Generic;

​

public abstract class Item

{

    public abstract void Use(); 

}

​

public class Potion : Item

{

    public override void Use()

    {

        // do nothing

        return;

    }

}

​

public class Sword : Item

{

    public override void Use()

    {

        Console.WriteLine("Sword used!");

        return;

    }

}

public class Program

{

    public static void Main()

    {

        List<Item> items = new List<Item>();

        Item potion = new Potion();

        Item sword = new Sword();

        items.Add(potion);

        items.Add(sword);

        for (int i = 0; i < items.Count; i++)

        {

            Item item = items[i];

            item.Use();

        }

    }

}