You stay behind

You stay behind and ask the Professor for a bit of..."incentive". She sits on top of her desk and spreads her legs before beckoning you over. You quickly pull down her panties before pulling out your cock and shoving it inside her. You desperately pound her pussy and begin to suck on her tits. Soon enough, your balls tighten and you unload inside her pussy. The Professor sends you on your way after assuring you there'll be more where that came from if you continue on your journey.