using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        long number = 12349874529768521;

        string result = BaseN.Encode(number);

        number = BaseN.Decode(result);

        Console.WriteLine(number);

        Console.WriteLine(result);

    }

​

    public static class BaseN

    {

        private const string CharList = "0123456789abcdefghijklmnopqrstuvwxyz";

        public static String Encode(long input)

        {

            if (input < 0)

                throw new ArgumentOutOfRangeException("input", input, "input cannot be negative");

            var result = new System.Collections.Generic.Stack<char>();

            while (input != 0)

            {

                result.Push(CharList.ToCharArray()[input % CharList.Length]);

                input /= CharList.Length;

            }

​

            return new string (result.ToArray());

        }

​

        public static long Decode(string input)

        {

            long result = 0, pos = 0;

            foreach (char c in input.Reverse())

            {

                result += CharList.IndexOf(c) * (long)Math.Pow(CharList.Length, pos);

                pos++;

            }

​

            return result;

        }

    }

}