Poland and Lithuania are coutries themselves, not parts of another.

Poland

Members of the Commonwealth of Independent States or CIS had all been formerly members of the USSR and the annexed countries. These annexed countries were Hungary, East Germany, Poland, or Lithuania.

the largest is Poland-Lithuania

The European countries that border the Baltic Sea are: Russia, Lithuania, Latvia, Poland, Germany, Sweden, Finland, Estonia, and Denmark.

Of those, Russia, Lithuania, Latvia, Poland, and Estonia are considered Eastern European. Germany is considered Western or Central European. Denmark, Sweden, and Finland are considered Scandinavian.