With a continuously running clock, squat for 60 seconds. Subtract the number of squats completed from 60, and do that many pull-ups in minute two. In minute three, squat again, subtracting the number completed from 60. Do that number of push-ups in minute four. Minute five is squatting again, and minute six pull-ups.
The pattern is squats, pull-ups, squats, push-ups, squats, pull-ups, etc. The goal is to stay within the workout's formula for as long as possible.
Don't do more than 60 squats in any round.
In any case, stay moving for at least 12 minutes.