Lithuania (Listeni/ˌlɪθuːeɪniə/; Lithuanian: Lietuva; [ˈliɛtʊvaː] ), officially the Republic of Lithuania (Lithuanian: Lietuvos Respublika), is a country in Northern Europe, one of the three Baltic states. It is situated along the southeastern shore of the Baltic Sea, to the east of Sweden and Denmark. It is bordered by Latvia to the north, Belarus to the east and south, Poland to the south, and Kaliningrad Oblast (a Russian exclave) to the southwest. Lithuania has an estimated population of 3 million as of 2013, and its capital and largest city is Vilnius. Lithuanians are a Baltic people. The official language, Lithuanian, and Latvian are the only two living languages in the Baltic branch of the Indo-European language family. For centuries, the southeastern shore of the Baltic Sea was inhabited by various Baltic tribes. In the 1230s, the Lithuanian lands were united by Mindaugas, the King of Lithuania, and the first unified Lithuanian state, the Kingdom of Lithuania, was created on 6 July 1253. During the 14th century, the Grand Duchy of Lithuania was the largest country in Europe; present-day Lithuania, Belarus, Ukraine, and parts of Poland and Russia were the territories of the Grand Duchy. With the Lublin Union of 1569, Lithuania and Poland formed a voluntary two-state union, the Polish–Lithuanian Commonwealth. The Commonwealth lasted more than two centuries, until neighboring countries systematically dismantled it from 1772–95, with the Russian Empire annexing most of Lithuania's territory. As World War I neared its end, Lithuania's Act of Independence was signed on 16 February 1918, declaring the establishment of a sovereign State of Lithuania. Starting in 1940, Lithuania was occupied first by the Soviet Union and then by Nazi Germany. As World War II neared its end in 1944 and the Germans retreated, the Soviet Union reoccupied Lithuania. On 11 March 1990, a year before formal break-up of the Soviet Union, Lithuania became the first Soviet republic to declare itself independent, resulting in the restoration of an independent State of Lithuania. Lithuania is a member of the European Union, the Council of Europe, a full member of the Schengen Agreement and NATO. It is also a member of the Nordic Investment Bank, and part of Nordic-Baltic cooperation of Northern European countries. The United Nations Human Development Index lists Lithuania as a "very high human development" country. Lithuania has been among the fastest growing economies in the European Union and is ranked 24th in the world in the Ease of Doing Business Index. On 1 January 2015, Lithuania adopted the euro as the official currency and became the 19th member of the Eurozone.