If students can not be noisy, have all their trash picked up afterward, and not enter other buildings during lunch, then they can eat on the hill outside the cafeteria.
Strong version of the same sentence is following;
If the students can not stay quiet, they will have to pick up the trash after them, they will not be allowed to enter any of the buildings for lunch and as a punishment, they can go eat their lunch on the hill outside the cafeteria.
