Are there any countries that enforce copyright as much as the US do? I have no idea when a book legally enters public domain in Russia, since any book I can think of is a couple clicks away. Literally anything: Nabokov, Rowling, etc
Edit: come to think of it, it's pretty universal. Libgen and bookfi are not exactly Russian. There's probably little difference whether a book is public domain unless you want to make a movie.