Hi, here's your problem today. This problem was recently asked by Apple:

In many spreadsheet applications, the columns are marked with letters. From the 1st to the 26th column the letters are A to Z. Then starting from the 27th column it uses AA, AB, ..., ZZ, AAA, etc.

Given a number n, find the n-th column name.

<pre lang=py>
def column_name(n):
  # Fill this in.

print column_name(26)
print column_name(27)
print column_name(28)
# Z
# AA
# AB
</pre>