Thanks. I see.

The input can't be 13.

and there is no 13th floor (due to superstition)

What if the input is 13? Then it doesn't even work. How can this be top solution? :D

I appreciated:

1. the spacing
2. that 13 as an input wasn't even considered! :-D

Very clear!

thank you for explanation

If it helps, list comprehension is of the form:

L = [A for x in X for y in Y for z in Z if B]

Which can be written as:

L = []
for x in X:
  for y in Y:
    for z in Z:
      if B:
        L.append(A)

You can put as many for as you want, and of course you can put list comprehension inside list comprehension:

L = [[A for x in X] for y in Y]

Which can be written as:

L = []
for y in Y:
  temp = []
  for x in X:
    temp.append(A)
  L.append(temp)

It took me some time to understand which for was done first when I started.