@Slav you are ONLY allowed to write on the exam booklet for your calculations, and of course you are also allowed to fill in your answer sheet. But they are very strict about the fact that you are NOT allowed to write anywhere else (e.g. exam ticket, scratch paper).
You are definitely NOT allowed to bring any extra paper into the exam room, and in fact doing so could get yourself disqualified from the exam.
There is enough space for writing calculations etc on the exam question booklet so you won’t run out of space.
Scribble away on the question paper. Don’t scribble anywhere else, including exam ticket, answer sheet, table, your palm, etc. The proctors are very strict about questionable behaviour and it seems that the only thing this results in is disqualification from the exam. Totally not worth fooling around.