@Semyon *******
I see. Hopefully you can change your ticket, but the lesson is, always plan to stay a little longer.
When I applied for my visa (in Taiwan) I had already planned on staying several days in order to travel as well.
I ended up staying 6 days and 6 nights but because I needed to submit additional documents on the second day (the day I would have otherwise received my visa) they only gave me my passport back the afternoon before my flight back (I flew out the next morning), which was the Monday following the weekend. Thus, I was without my passport for most of the trip (although that was fine; I didn't need it for hotel check-in and copies of the important pages was sufficient to rent a car).
I was pretty sure I'd be fine, but if for some reason I had to submit even more documents, I would have had to spend another 3-4 days longer, since there was also a public holiday 2 days later.