Firstly I had to do an exercise from 1st stage of Informatics Olympiad, then an exercise from 3rd stage of Informatics Olympiad. In the end I was invited to write both of these exercises and one other which was very easy in their office without the permission to use internet.

the interview process has 2 steps. On the first one you need to write 2 easy problems. On the second step they verify your english skills and ask about your technical knowledge.