# Problem Definition

## Description

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

```test
    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB
```

## Notes

This is just like base 26 number conversion.

Think of it like this. How would you convert a number to binary ? Can you apply the same principle here now that the base is different ?