Spend 15 minutes on Handstands
Beginners– just spend time upside down, use a box, the wall, whatever but support as much of your own weight upside down as you can.
Intemediate– work on handstand push ups. Scale to whatever height of abmats under your head you can successfully get to. Try to lower that over the 15 minutes.
Advanced– Go for 2 handstand push ups every minute on the minute.