Grab and ab-mat (you can buy one online here for next time), and do 300 sit ups as fast as possible, which probably won't be very fast.
Your abs will thank me tomorrow... ok actually probably next week after they stop hating me.
BUT
If you want a real workout, do 400 meters (one lap) of walking lunges. Remember full extension on each one.
Please don't hate me if you do both of these, because you WILL be sore!
