There is no such country and therefore no such capital.
If perhaps you meant to ask about the Mediterranean and Black Seas, the answer would be Turkey.
If perhaps you meant to ask about the Baltic and Black Seas, the answer is Russia.
Copenhagen
There is no such country.
No, Poland doesnt border any country with a coastline on the Mediterranean Sea, the countries that Poland borders have either a coastline on the North sea or the Baltic sea.
The Baltic is a sea and not a country
poland
Helsinki, the capital and largest city of Finland, borders the Gulf of Finland and the Baltic Sea.
The country that is south of Latvia and has a coastline on the Baltic Sea is Lithuania. Its capital is Vilnius.
Latvia
Russia.
Vilnius is the capital city of Lithuania, the country that is south of Latvia and has a coastline on the Baltic Sea.
Both Sweden and Finland
poland
Germany is the only country that borders Denmark and it is to the south of the country. Denmark is bordered by the Baltic Sea to the east.