Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. Bulgaria borders five other countries: Romania to the north (mostly along the Danube), Serbia and the Republic of Macedonia to the west, and Greece and Turkey to the south. The Black Sea defines the extent of the country to the east. With a territory of 110 994 square kilometers (42 855 sq mi), Bulgaria ranks as the 16th-largest country in Europe. Several mountainous areas define the landscape, most notably the Stara Planina (Balkan) and Rodopi mountain ranges, as well as the Rila range, which includes the highest peak in the Balkan region, Musala. In contrast, the Danubian plain in the north and the Upper Thracian Plain in the south represent Bulgaria's lowest and most fertile regions. The 378-kilometer (235 mi) Black Sea coastline covers the entire eastern bound of the country. Bulgaria's capital city and largest settlement is Sofia. Bulgaria functions as a parliamentary democracy within a unitary constitutional republic. A member of the European Union, NATO, the United Nations, the Council of Europe, the World Trade Organization and a founding state of the OSCE and the Black Sea Economic Cooperation Organization, it has a high Human Development Index of 0.743, ranking 58th in the world in 2010. The economy of Bulgaria is an industrialised, free market economy with steadily growing tourism sector and a moderately advanced private sector. Bulgaria is an upper-middle-income country according to the World Bank with a gross national income per capita of US$ 5 490 in 2008. The country is expected to join the Eurozone in 2013 and has implemented all criteria for joining the Schengen Area according to the European Council.The country benefits from rich natural resources, a highly educated population and an export-oriented agricultural sector. On 1 January 2007 Bulgaria entered the European Union. This led to some immediate international trade liberalization, but there was no shock to the economy. The government is running annual surpluses of above 3%. This fact, together with annual GDP growth of above 5%, has brought the government indebtedness to 22.8% of GDP in 2006 from 67.3% five years earlier. This is to be contrasted with enormous current account deficits. Low interest rates guaranteed availability of funds for investment and consumption.