Ukraine, republic in eastern Europe, bordered on the north by Belarus and Russia; on the east by Russia; on the south by the black Sea and the Sea of Azov; on the south-west by Romania and Moldova; and on the west by Hungary, Slovakia, and Poland. Formerly the Ukrainian Soviet Socialist Republic (SSR) of the Union of Soviet Socialist Republics (USSR), Ukraine is an associate member of the Commonwealth of Independent States (CIS), which in December 1991 succeeded the USSR. It has withheld its agreement on payments and customs union, choosing "observer" status at the CIS Intergovernmental Assembly. With a total area of about 603,700 sq km (233,090 sq mi), Ukraine is the second-largest nation in Europe after Russia.