using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string pattern = @"\$[a,f]+";

        string input = "$aThe $ 30,000 Bequest and Other Stories$fM. Twain";

        string[] result = Regex.Split(input, pattern, 

                                        RegexOptions.IgnoreCase,

                                        TimeSpan.FromMilliseconds(500));

        for (int ctr = 0; ctr < result.Length; ctr++) {

            Console.Write("'{0}'", result[ctr]);

            if (ctr < result.Length - 1) 

                Console.Write(", ");

        }

        Console.WriteLine();

    }

}