using System;

public class Program

{

    public static void Main()

    {

        //dateTime = dateTime.AddTicks( - (dateTime.Ticks % TimeSpan.TicksPerSecond))

        var dateTime = DateTime.Now;

        var dateTime2 = dateTime.AddTicks(-(dateTime.Ticks % TimeSpan.TicksPerMillisecond));

        Console.WriteLine(dateTime.ToString("ss.fffffff"));

        Console.WriteLine(dateTime2.ToString("ss.fffffff"));

        Console.WriteLine(dateTime.Millisecond);

        Console.WriteLine(dateTime2.Millisecond);

        Console.WriteLine(dateTime.Ticks);

        Console.WriteLine(dateTime2.Ticks);

    }

}