In site my script fails on case "Lorem ipsum dolor sit amet". It says that my script returns 0, while right answer is "m". But I've tried it in IDLE. This case works.

From: https://checkio.org/mission/most-wanted-letter/solve/

HTTP_USER_AGENT:

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.86 Safari/537.36