On 25 October 1992, the citizens of Lithuania voted in a referendum to adopt the current constitution. On 14 February 1993, during the direct general elections, Algirdas Brazauskas became the first president after the restoration of independence of Lithuania. On 31 August 1993 the last units of the Soviet Army left the territory of Lithuania. On 31 May 2001, Lithuania joined the World Trade Organization (WTO). Since 29 March 2004, Lithuania has been part of the NATO. On 1 May 2004, it became a fully-fledged member of the European Union, and a member of the Schengen Agreement on 21 December 2007. On 1 January 2015, Lithuania joined the eurozone and adopted the European Union's single currency as the last of the Baltic states. On 4 July 2018, Lithuania officially joined OECD.