using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        const string format = "yyyy-MM-dd hh:mm tt";

        CultureInfo enUS = new CultureInfo("en-US"); 

        string dateString = DateTime.Now.ToString(format);

        DateTime? result;

        DateTime parseResult;

        if (DateTime.TryParseExact(dateString, format, enUS, DateTimeStyles.None, out parseResult)) {

            result = parseResult;

        }

        else {

            result = null;

        }

        Console.WriteLine(result.HasValue ?  result.Value.ToString(format) : "null");

    }

}