If you are walking straight and not disturbing anyone, the police will likely just ignore you. However, if you have a questionable appearance - think dirty, soiled, foul smelling clothes and unnecessarily exposed patches of skin - or you are swaying, swearing and falling down, expect some form of punishment. Usually the punishment is fairly mild. For example, if policemen pick you up off a street, they typically just keep you at the station for a couple of hours so that you can sleep it off, check your documents and release you. All the same, there is no guarantee that the punishment will not be more severe, so do all you can to avoid contact with police while in Russia.