My solution is 20 lines.
Easy problem.

14 lines solution with using recursive function.

I have recursive function too.
Whatever, Good Job!

7 lines with recursive func in python 3.
Or 14 with normal look a code.

5 lines

I got by 2 lines
But It possible by 1 using https://overcoder.net/q/87149/может-ли-лямбда-функция-вызывать-себя-рекурсивно-в-python (rus forum)