Madonna is already getting the hang of this Instagram thing. She only just recently opened her account and she's already posted a shot of her heaving bosom -- and now her ass cheeks, too.

Let's hope she doesn't see Rihanna's page and feel the need to compete. This could get ugly.

On Wednesday, she posted the photo here along with the caption, “Working on the edit of the live concert!”

Madge is no stranger to showing off her body parts. Everyone knows about her 'Sex' book from the early '90s, but as recently as last year the 54-year-old flashed global audiences with her bare boobs and backside while on tour.

At least her official social media stuff is (thus far) not quite so risque. But we have the feeling that won't last.