Add OnrollOut function in a button

Hi all,
i have created a 5th frame inside a button (with a movie clip in it) for my OnRollOut function.

But i dont know where to put the action script for read my 5th frame when my mouth roll out the button.

my action script look like.

on (rollout) {
gotoandplay (5) ; <— “for the 5th frame”

but i doesnt play my mc animation.
Thanks for any helps.