Roberto is shopping in a large department store with many floors. He enters the store on the middle floor from a skyway and immediately
goes to the credit department. After making sure his credit is good, he
goes up three floors to the housewares department. Then he goes down
five floors to the children's department. Then he goes up six floors to the
TV department. Finally, he goes down ten floors to the main entrance of
the store, which is on the first floor, and leaves to go to another store
down the street. How many floors does the department store have?