using System;
using System.Text.RegularExpressions;

namespace RegexAABBCC
{
    class Program
    {
        static void Main(string[] args)
        {
            string re = @"(?:(?(1)(?!))(hell)|(?(2)(?!))(hello)|(?(3)(?!))(foo))+";
            
            string[] txt = {
                "foo",
                "hellhello",
                "foohellohell",
                "hellhellohell",
                "foohellohellfoo",
            };

            foreach (string s in txt)
            {
                Match m = Regex.Match(s, re);

                if (m.Success == true)
                {
                    Console.WriteLine("Matched:     \"{0}\" \tin: \"{1}\"", m.Value, s);
                }
                else
                {
                    Console.WriteLine("Not matched: \"{0}\"", s);
                }
            }

            Console.ReadKey();
        }
    }
}