using System;

using System.Security.Cryptography;

using System.Linq;

using System.Globalization;

​

public class Program

{

         public static string CorrectRRULE(string rrule)

        {

            return rrule.Split(" ").Skip(1).FirstOrDefault() ?? rrule;

        }

    public static void Main()

    {

         var rrulePurged = "DTSTART=20221129T1430000Z RRULE:UNTIL=20230228T150000Z;INTERVAL=1;FREQ=DAILY;WKST=MO".Split(" ").Skip(1).FirstOrDefault();   

         var recurrenceEvaluator = new Ical.Net.Evaluation.RecurrencePatternEvaluator(new Ical.Net.DataTypes.RecurrencePattern(rrulePurged));

​

         var recurrentPattern = new Ical.Net.DataTypes.RecurrencePattern(rrulePurged);

         Console.WriteLine(recurrentPattern.Until);

    }

​

}