Clip 5 clothes pegs onto each tit, one on each nipple and the rest spread around. Now you do push ups, for each 10 you finish you may remove 1 peg from each tit until you have finished 50 push ups. If you cant make the 50 and you stop at any point (a brief pause is allowed to remove the pegs) then you must sit out the remaining time as 10 minutes for every peg left on your tits. During the "sit out" time penalty you must sit with your hands on head and simply wait it out.
If you can complete this, or even if you cant, I have plenty more exercise tasks.