using System;

public class Program

{

    public static void Main()

    {

        var currentDateTime = DateTime.Now;

        var previousDatetime = DateTime.Now.AddMilliseconds(0);

        var diff = currentDateTime.Subtract(previousDatetime).Milliseconds;

​

        var result = diff > 0 ? "Greater" : 

                     diff == 0 ? "equal" : "Less than";

        Console.WriteLine("Current date time is " + result +" previous date time");

    }

}