using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		Regex regex = new Regex("(([_ ]*[a-z]+)_ ?)+([_ ]*[a-z]+)");
            string str = "a_b_c_ _ _abc_ _ _ _abcd";

            Match match = regex.Match(str);
            for (int i = 2; i < match.Groups.Count; i++) {

                foreach (Capture capture in match.Groups[i].Captures)
                    Console.Write("[{0}]", capture.Value);
            }

            Console.ReadLine();
	}
}