After I went to bed it hit me too... Still don't understand how can it be that it sometimes passes that particular test, sometimes it isn't (I'm not changing the code, just spamming the 'Attempt' button). Anyway, thanks for your reply!

The line is printed many times because there is many tests and your solution is called more than once.

Indeed. Had to ask an AI what the problem actually wants from me :D (not for the solution, just for a clear description)

Your solution is not exactly correct. It incorrectly recognizes some non-square numbers as squares, for example 114 or 155.

One of the test cases (89) return 136 instead of -1. In my IDE (Eclipse) works just fine. Am I missing something?

Having to deal with the case where nothing is passed in as a parameter was just annoying.