Nigeria is a federal republic in West Africa, bordering Benin in the west, Chad and Cameroon in the east, and Niger in the north. Its coast in the south lies on the Gulf of Guinea in the Atlantic Ocean. With approximately 184 million inhabitants, Nigeria is the most populous country in Africa and the seventh most populous country in the world. As of 2015, Nigeria is the world's 20th largest economy, worth more than $500 billion and $1 trillion in terms of nominal GDP and purchasing power parity respectively. It is the second-largest economy in Africa, after South Africa.