count (me/us) in

When someone invites you to participate, you can say "yes" with the phrase "count me in":

A: I feel really good about this business opportunity so I was hoping that you'd be interested in investing.

B: Yeah, count me in.

Or you can speak for yourself and someone else, like your partner or friends:

If you guys ever decide to organize a camping trip, definitely count us in.

This phrase appears in these lessons: