Greece, also known as Hellas and officially the Hellenic Republic, is a country in southeastern Europe, situated on the southern end of the Balkan Peninsula. The country has land borders with Albania, the Republic of Macedonia and Bulgaria to the north, and Turkey to the east. The Aegean Sea lies to the east of mainland Greece, the Ionian Sea to the west, and the Mediterranean Sea to the south. Greece has the tenth longest coastline in the world at 14, 880 km (9, 246.00 mi) in length, featuring a vast number of islands (approximately 1400, 227 of which are inhabited), including Crete, the Dodecanese, the Cyclades, and the Ionian Islands among others. Eighty percent of Greece consists of mountains, of which Mount Olympus is the highest at 2, 917 m (9, 570.21 ft). Modern Greece traces its roots to the civilization of ancient Greece, generally considered to be the cradle of Western civilization. As such, it is the birthplace of democracy, Western philosophy, the Olympic Games, Western literature and historiography, political science, major scientific and mathematical principles, and Western drama, including both tragedy and comedy. This legacy is partly reflected in the 17 UNESCO World Heritage Sites that Greece is home to. A developed country with a very high Human Development Index, Greece has been a member of what is now the European Union since 1981 and its Economic and Monetary Union since 2001, NATO since 1952, and the European Space Agency since 2005. It is also a founding member of the United Nations, the OECD, and the Black Sea Economic Cooperation Organization. Athens is the capital; other major cities include Thessaloniki, Patras, Heraklion and Larissa.