02.09.01.01.KaspichanNumber

using System;
using System.Collections.Generic;

class KaspichanNumber
{
    static void Main()
    {
        ulong input = ulong.Parse(Console.ReadLine());
        ulong numSystem = 256;
        List<ulong> listNumbers = ConvertToAny(input, numSystem);
        List<char> charNumbers = ConvertToChar(listNumbers);
        foreach (var ch in charNumbers)
        {
            Console.Write(ch);
        }
    }

    private static List<ulong> ConvertToAny(ulong number, ulong numSystem)
    {
        List<ulong> listNumbers = new List<ulong>();
        if (number == 0)
        {
            listNumbers.Add(0);
        }

        while (number > 0)
        {
            listNumbers.Add(number % numSystem);
            number = number / numSystem;
        }

        listNumbers.Reverse();

        return listNumbers;
    }

    private static List<char> ConvertToChar(List<ulong> listNumbers)
    {
        List<char> listChars = new List<char>();
        foreach (ulong numb in listNumbers)
        {
            List<ulong> listNumbers26 = new List<ulong>();
            ulong temp = numb;
            if (temp == 0)
            {
                listNumbers26.Add(0);
            }

            while (temp > 0)
            {
                listNumbers26.Add(temp % 26);
                temp = temp / 26;
            }
            //listNumbers26.Reverse();
            for (int i = listNumbers26.Count - 1; i >= 0; i--)
            {
                if (i == 1)
                {
                    listChars.Add((char)(listNumbers26[i] + 96));
                }
                else
                {
                    listChars.Add((char)(listNumbers26[i] + 65));
                }
            }

        }
        return listChars;
    }
}