using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var text = "blah blah this is a this search engine blah";
		var result = Regex.Match(text, @"this.*?engine", 
			RegexOptions.Singleline | RegexOptions.RightToLeft)?.Value;
        Console.WriteLine(result);
	}
}