using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var CurrentDate = DateTime.Now;

        DateTime periodEndDate = CurrentDate.AddMonths(1).AddDays(-(CurrentDate.AddMonths(1).Day));

        List<DateTime> periodEndDates = new List<DateTime>();

        periodEndDates.Add(Convert.ToDateTime("2018-01-02T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-01-31T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-02-28T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-04-02T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-04-30T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-05-31T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-07-02T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-07-31T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-08-31T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-10-01T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-10-31T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2018-11-30T00:00:00"));

        periodEndDates.Add(Convert.ToDateTime("2019-01-02T00:00:00"));

        //CurrentDate = Convert.ToDateTime("2018-10-31T18:34:00");

        CurrentDate = Convert.ToDateTime("2018-11-01T00:00:00");

        if (periodEndDates.Count > 0)

        {

            TimeZoneInfo pstZone = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");

            // Convert current date to PST

            CurrentDate = TimeZoneInfo.ConvertTimeFromUtc(CurrentDate, pstZone);

​

            var tryDate = periodEndDates.OrderBy(d => d).FirstOrDefault(d => d.Date >= CurrentDate.Date);

            var oldTryDate = periodEndDates.OrderBy(d => d).FirstOrDefault(d => d >= CurrentDate);

            Console.WriteLine("tryDate -->" + tryDate);

            Console.WriteLine("oldTryDate -->" + oldTryDate);

            if (tryDate != DateTime.MinValue && tryDate != DateTime.MaxValue)

            {

                periodEndDate = tryDate;

            }

        }

    }

}