Ireland, also known as the Republic of Ireland, is a sovereign state in north western Europe occupying about five-sixths of the island of Ireland. The capital and largest city is Dublin, located in the eastern part of the island, whose metropolitan area is home to around a third of the country's 4.6 million inhabitants. The state shares its only land border with Northern Ireland, a part of the United Kingdom. It is otherwise surrounded by the Atlantic Ocean, with the Celtic Sea to the south, Saint George's Channel to the south east, and the Irish Sea to the east. It is a unitary, parliamentary republic with an elected president serving as head of state. The head of government, the Taoiseach, is nominated by the lower house of parliament, Dáil Éireann.