➜ cat test.cpp
#include <iostream>
#include <cstdint>


// Is translation from 2-position to 26-position notation
//
// X - bit count in source
// Y - position count in result
//
// sizeof(T) = log(base=2, number=X)
// X = power(2, sizeof(T))
// Y = log(base=26, number=X)
// Y = log(base=26 number=power(2, sizeof(T)))
// Y = sizeof(T) * log(base=26, number=2)
//
// python:
//  >>> math.log(2, 26)
//  0.21274605355336315
//
// Y ~ = sizeof(T) / 4

typedef uint64_t Type;
typedef uint8_t Result[sizeof(Type) / 4];

uint8_t toExcel(Type input, Result* result)
{
    uint8_t position = 0;
    do
    {
        (*result)[position++] = input % 26;
        input = input / 26;
    }
    while (input > 0);
    return position;
}


void printResult(Type input, Result* result, uint8_t length)
{
    std::cout << input << "\t";
    std::string string;
    for(uint8_t i = length; i > 0; --i)
        string += 'A' + (*result)[i - 1] - (i == 1 ? 0 : 1);
    std::cout << string;
    std::cout << std::endl;
}


int main(int, char*[])
{
    uint64_t input;
    Result result;
    while (std::cin >> input)
    {
        if (input == 0)
            continue;
        uint8_t length = toExcel(input - 1, &result);
        printResult(input, &result, length);
    }
    return 0;
}
otsarev@tsarev-desktop:~ ─────────────────────────────────────────────────────────────────────────────────
➜ g++ ./test.cpp --std=c++11
otsarev@tsarev-desktop:~ ─────────────────────────────────────────────────────────────────────────────────
➜ echo "0 1 2 3 25 26 27 28 51 52 53 12312" | ./a.out
1	A
2	B
3	C
25	Y
26	Z
27	AA
28	AB
51	AY
52	AZ
53	BA
12312	REN