You answer:

I watched the movie a couple of times in Soviet times, but I don't know the title. And the worst thing is that I don't remember any of the famous actors there. Or you can find the last name on Kinopoisk.
So the plot... there was this guy who could do calculations and multiplications in his head. And a guy gave him a wristwatch. And then they disagreed and the guy started beating him up and said, "Now let's multiply...".
I think there was something mentioned about Pushkin...