Sit on the edge of your chair, hands outside of hips on the edge of the seat. Press your knees together, bring your legs to the right corner of the chair, and lift your heels. Brace your abs in tight and lift your legs (keeping knees bent and together) and trace a half circle so that your legs land at the left corner of the chair. Repeat, alternating sides each time, for a total of 20 reps.
Form tip: Try not to let your back round as you lift your legs, and focus on pulling your belly button into your spine as you circle your legs back and forth.