Multiverse Communication

using System;
using System.Collections.Generic;
using System.Text;
using System.Numerics;

namespace MultiverseCommunicationFIXED
{
    class Program
    {
        static BigInteger Repeater(int times)
        {
            BigInteger result = 1;

            for (int s = 0; s < times; s++)
            {
                result *= 13;
            }

            return result;
        }

        static void Main()
        {
            string input = Console.ReadLine();
            string[] workput = new string[input.Length / 3];
            int count = 0;
            BigInteger sum = 0;
            string workNumber = string.Empty;
            BigInteger modifier = 1;

            for (int i = 0;  i < input.Length; i++)
            {
                if (i % 3 == 0 && i != 0)
                {
                    count++;
                }
                workput[count] += input[i];
            }

            for (int i = 0; i < workput.GetLength(0); i++)
            {
                switch (workput[i])
                {
                    case "CHU":
                        workNumber += 0.ToString();
                        break;
                    case "TEL":
                        workNumber += 1.ToString();
                        break;
                    case "OFT":
                        workNumber += 2.ToString();
                        break;
                    case "IVA":
                        workNumber += 3.ToString();
                        break;
                    case "EMY":
                        workNumber += 4.ToString();
                        break;
                    case "VNB":
                        workNumber += 5.ToString();
                        break;
                    case "POQ":
                        workNumber += 6.ToString();
                        break;
                    case "ERI":
                        workNumber += 7.ToString();
                        break;
                    case "CAD":
                        workNumber += 8.ToString();
                        break;
                    case "K-A":
                        workNumber += 9.ToString();
                        break;
                    case "IIA":
                        workNumber += "A";
                        break;
                    case "YLO":
                        workNumber += "B";
                        break;
                    case "PLA":
                        workNumber += "C";
                        break;
                }
                modifier *= 13;
            }

            for (int j = workNumber.Length - 1, x = 0; j >= 0; j--, x++)
            {
                BigInteger stepen = Repeater(x);

                switch (workNumber[j])
                {
                    case '0':
                        sum += 0 * stepen;
                        break;
                    case '1':
                        sum += 1 * stepen;
                        break;
                    case '2':
                        sum += 2 * stepen;
                        break;
                    case '3':
                        sum += 3 * stepen;
                        break;
                    case '4':
                        sum += 4 * stepen;
                        break;
                    case '5':
                        sum += 5 * stepen;
                        break;
                    case '6':
                        sum += 6 * stepen;
                        break;
                    case '7':
                        sum += 7 * stepen;
                        break;
                    case '8':
                        sum += 8 * stepen;
                        break;
                    case '9':
                        sum += 9 * stepen;
                        break;
                    case 'A':
                        sum += 10 * stepen;
                        break;
                    case 'B':
                        sum += 11 * stepen;
                        break;
                    case 'C':
                        sum += 12 * stepen;
                        break;
                }
            }

            Console.WriteLine(sum);
        }
    }
}