using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        double what = 17.999;

        double what1 = 17.9;

        Console.WriteLine(what.ToString("F3", CultureInfo.InvariantCulture));

        Console.WriteLine(what.ToString("N3", CultureInfo.InvariantCulture));

        Console.WriteLine(what1.ToString("F3", CultureInfo.InvariantCulture));

        Console.WriteLine(what1.ToString("N3", CultureInfo.InvariantCulture));

    }

}