using System;
using System.Collections.Generic;

internal static class Program
{
    private static void Main(string[] args)
    {
        var codes = new HashSet<string>(StringComparer.Ordinal) { "W-17" };
        Console.WriteLine($"Duplicate added: {codes.Add("W-17")}");
        Console.WriteLine($"New added: {codes.Add("W-18")}");
        Console.WriteLine($"Unique codes: {codes.Count}");
    }
}