using System;
using System.Globalization;
 
public class Example
{
   public static void Main()
   {
      string dateString, format;  
      DateTime result;
      CultureInfo provider = new CultureInfo("en-US"); 
 
      string lastUpdatedDate = "20150219T045452:635599184921416348";
      string[] parse = lastUpdatedDate.Split(':');
      lastUpdatedDate = parse[0] + ":" + parse[1].Substring(0,3);
      DateTime dt = DateTime.ParseExact(lastUpdatedDate,"yyyyMMddTHHmmss:fff",provider);
   }
}
 

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