using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
string pattern = @"X([^X]+)";
string input = @"X
aaaa
X
bbbb
X
cccc";

foreach (Match m in Regex.Matches(input, pattern))
{
    Console.WriteLine(m.Groups[1].Value.Trim());
}
    }
}