context: Legislative power in Warsaw is vested in a unicameral Warsaw City Council (Rada Miasta), which comprises 60 members. Council members are elected directly every four years. Like most legislative bodies, the City Council divides itself into committees which have the oversight of various functions of the city government. Bills passed by a simple majority are sent to the mayor (the President of Warsaw), who may sign them into law. If the mayor vetoes a bill, the Council has 30 days to override the veto by a two-thirds majority vote.
question: How often are elections for the mayor held?