The government of the Marshall Islands operates under a mixed parliamentary-presidential system as set forth in its Constitution. Elections are held every four years in universal suffrage (for all citizens above 18), with each of the twenty-four constituencies (see below) electing one or more representatives (senators) to the lower house of RMI's unicameral legislature, the Nitijela. (Majuro, the capital atoll, elects five senators.) The President, who is head of state as well as head of government, is elected by the 33 senators of the Nitijela. Four of the five Marshallese presidents who have been elected since the Constitution was adopted in 1979 have been traditional paramount chiefs.