using System;
public class DateTimeUtils
{
public static DateTime RoundDown(DateTime dt, TimeSpan d)
return new DateTime((dt.Ticks / d.Ticks) * d.Ticks);
}
public class Program
public static void Main()
var dt1 = DateTimeUtils.RoundDown(DateTime.UtcNow, TimeSpan.FromMinutes(30));
Console.WriteLine(dt1);