Apparently in 2009 Obama visited Moscow and managed to meet both president Putin and president Medvedev. Granted, it is sometimes hard to remember who of these two is a president at any given moment, but a two-president state is a bit pushing it.
Where I live, Finland, a "President" is the official title for former presidents (there are now three alive) so I should actually address them as such. The current one is formally referred to as "President of the Republic". I can't really check how this is with Russia.
I'm not convinced. Multiple other sources say you retain the title for life and also recommend addressing the person as such. Obviously it's a matter of etiquette and not right or wrong, though.
