Senegal is a country in western Africa with an Atlantic Ocean coastline. Neighboring countries include The Gambia, Guinea, Guinea-Bissau, Mali, and Mauritania. Senegal's geography is mostly flat, and the northern border is formed by the Senegal River. The government system is a republic; the chief of state is the president, and the head of government is the prime minister. Senegal has a mixed economic system in which the presence of the state in the economy is considerable, but there is limited private sector freedom. Senegal is a member of the Economic Community of West African States (ECOWAS).