using System;

public class Program

{

    public static void Main()

    {

        var localDeadline = new DateTime(2017,7,6,   12,00,00);

        var localNow = new DateTime(2016,7,5,   18,00,00);

        string result;        

                var timeToDeadline = (localDeadline - localNow).Duration();

                if (timeToDeadline < TimeSpan.FromHours(24))

                    result = localDeadline.ToString("HH:mm");

                else if (timeToDeadline < TimeSpan.FromDays(DateTime.IsLeapYear(localNow.Year) ? 366 : 365))

                    result = localDeadline.ToString("dd-MMM");

                else

                    result = localDeadline.Year.ToString();

        Console.WriteLine(result);

    }

}