using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		var s = "hello 'world' hehe";
        var m = Regex.Match(s, "'([^']*)'");
        string res = null;
        if (m.Success) {
            res = m.Groups[1].ToString();
        }
        Console.WriteLine(res);        
	}
}