using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        decimal[] values =

        {

            500000M,

            500000.9M,

            500000.90M,

            500000.900M,

            500000.9000M,

            500000.99M,

            500000.999M,

            500000.9999M,

        };

        foreach (decimal d in values)

        {

            Console.WriteLine("{0,-15}{1}", d.ToString(), FormatDecimal(d));

        }

    }

    public static string FormatDecimal(decimal d)

    {

        string s = d.ToString("0.00##", NumberFormatInfo.InvariantInfo).Replace(".", ",");

        if (s.EndsWith(",00", StringComparison.Ordinal))

            s = s.Substring(0, s.Length - 2);

        return s;

    }

}