Lie on your back, and open your legs into a diamond shape (aka butterfly legs) with the soles of your feet pressed together and knees out wide. Extend the arms overhead.
Inhale to curl the torso up, and tap the floor in front of your feet to stretch your glutes a bit.
Slowly lower back to the starting position.
This counts as one rep.
Do as many reps as you can for 40 seconds, then rest for 20 seconds.