Something is wrong with your validator

I would like to give some feedback about ... - I created my script, then when I test my code in tester #4, show an advice: "your result is 4, the correct is 5", but I print the return and it is 5... WTF! - I attach the screenshot with this problem

From: http://www.checkio.org/mission/break-rings/solve/

HTTP_USER_AGENT: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:40.0) Gecko/20100101 Firefox/40.0