D9-P2.cs

   static void Main(string[] args)
        {
            string path = "../../input.txt";
            String input = File.ReadAllText(path);
            Console.WriteLine(getLength(input));
            Console.Read();
        }

        static long getLength(string input)
        {
            if (!input.Contains('('))
                return input.Length;
            long fullcount = 0;
            int i = 0;
            while (i < input.Length)
            {
                if (input[i] != '(') { i++; fullcount++; continue; }

                int length = Convert.ToInt32(input.Substring(i + 1, input.IndexOf('x', i) - i - 1));
                int count = Convert.ToInt32(input.Substring(input.IndexOf('x', i) + 1, input.IndexOf(')', i) - input.IndexOf('x', i) - 1));
                int clength = 3 + count.ToString().Length + length.ToString().Length;
                string part = input.Substring(i + clength, length);
                fullcount += getLength(part) * count;
                i += clength + length;
            }
            return fullcount;
        }