gistfile1.txt

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

class Program
{
    private static ulong ConvertFromBaseToDecimalNumber(string message, uint numeralSystem)
    {
        ulong power = 1;
        ulong decimalNumber = 0;
        for (int i = message.Length - 1; i >= 0; i--)
        {
            char symbol = message[i];
            if (symbol >= '0' && symbol <= '9')
            {
                decimalNumber += (ulong)(symbol - '0') * power;
            }
            else
            {
                decimalNumber += (ulong)(symbol + 10 - 'A') * power;
            }

            power *= numeralSystem;
        }

        return decimalNumber;
    }

    static void Main()
    {
        string input = Console.ReadLine();

        List<string> digits = new List<string>() { "CHU", "TEL", "OFT", "IVA", "EMY", "VNB", "POQ", "ERI", "CAD", "K-A", "IIA", "YLO", "PLA" };

        StringBuilder message = new StringBuilder();
        for (int i = 0; i < input.Length - 2; i += 3)
        {
            string subStr = input.Substring(i, 3);
            int digit = digits.IndexOf(subStr);
            if (digit >= 10)
            {
                message.Append(((char)(digit - 10 + 'A')).ToString());
            }
            else
            {
                message.Append(digit.ToString());
            }
        }

        ulong decimalNumber = ConvertFromBaseToDecimalNumber(message.ToString(), 13);
        Console.WriteLine(decimalNumber);
    }
}