How to (accurately) fill a space between three circles with another circle...?!

Hi there.

A geometry / alignment issue...

Please see the attached screenshot — if I have an arrangement of circles, I'd love to know if there's a script / tool / technique that will accurately plot a circle that is accurately placed, touching the three cirles around it and filling / fitting the space between its neighbours.

As shown by the red circles here! (These circles made by hand, they arent fitting correclty when you zoom in...)

thanks for your time!

ur