You can buy bus tickets at Tabacchi stores (indicated with a large T sign). Each ticket costs 1.50 euro. You can also buy the ticket from the bus driver but in this case it costs 2.50 euro. Your ticket is valid only once it has been stamped in the machine inside the bus (near the front entrance oo the bus). Each ticket is valid for 90 minutes from the moment you stamp it. You do not need to re-stamp your ticket if you switch buses.