using System;

using System.Data.SqlTypes;                 

public class Program

{

    public static void Main()

    {

        var date=DateTime.Parse("2017-07-07 23:58:59.999");

        var x=new SqlDateTime(date).Value;

        Console.WriteLine(date.ToString("yyyy-MM-dd HH:mm:ss.fff"));

        Console.WriteLine(x.ToString("yyyy-MM-dd HH:mm:ss.fff"));

    }

}