It is part of Russia.
Because the victorious Allies of World War 2 wanted it that way that Prussia is part of Poland, Russia, and Lithuania.
The part of Russia between Poland Lithuania is Kaliningrad, now known as Kaliningrad Oblast. It is also located near the Baltic Sea.
Kaliningrad:(part of Russia) and Lithuania
Kaliningrad
Kaliningrad
Kaliningrad Oblast
The Enclave of Kaliningrad
The enclave of Kaliningrad
Kaliningrad
The military operation known as blitzkrieg was developed by Heinz Guderian of the German Army. Guderian lived from 1888-1954 and lead troops in Poland, France, and Russia.
Poland and Russia belong to the Northern and Eastern Hemispheres.