Feedback from user lehmannro
The test checkio([1000000, ...]) violates the precondition that 0 <= |X| <= 1000, no?
URL from: http://www.checkio.org/mission/non-unique-elements/solve/
HTTP_USER_AGENT: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20140319 Firefox/24.0 Iceweasel/24.4.0
URL from: http://www.checkio.org/mission/non-unique-elements/solve/
HTTP_USER_AGENT: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20140319 Firefox/24.0 Iceweasel/24.4.0