Turkey
japan
The Arctic Ocean borders Asia in the north.
Europe and Asia are both continents, not countries. And Bulgaria is a country in the continent of Europe.
Russia is partly in Europe and partly in Asia, along with Turkey.
ASIA
Malaysia, which is in Asia.
Russia is itself partly European and partly Asian, so must be closest! Turkey is mostly in Asia but has a small part in Europe.
Asia is a continent and Russia is a country, Bashkortostan is in Russia and borders Europe and Asia.
There is no country that borders all three countries.
From a geological point of view, Turkey is unique in that it has landmass in both Europe and Asia. Could you not argue Russia borders both Europe & Asia?
Bulgaria isn't even on Asia...