using System;

internal static class Program
{
    private static void Main(string[] args)
    {
        IFeePolicy regular = new RegularFee();
        IFeePolicy supported = new SupportedFee();
        Console.WriteLine($"Regular units: {regular.Units(3)}");
        Console.WriteLine($"Supported units: {supported.Units(3)}");
    }
}

internal interface IFeePolicy { int Units(int places); }
internal sealed class RegularFee : IFeePolicy { public int Units(int places) => places * 2; }
internal sealed class SupportedFee : IFeePolicy { public int Units(int places) => places; }