using System;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var str = @"1. message: this is some message 2. message: this is some message 3. message: this is message which i want to see only in results";
 
		foreach (var message in Regex.Split(str, @"\d+\. message: ")
		    .GroupBy(m => m)
		    .Where(m => m.Count() == 1 && m.Key != string.Empty)
		    .Select(m => new { message = m.Key }))
		{
 
		    Console.WriteLine(message.message);
		}
	}
}

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