Two Objects Following Each Other While Maintaining Minimum Distance

Hello,

I'm trying to solve a problem where I have one circle following another ( the first following the mouse ), yet maintain a minimum distance between the two circles.

The code is pretty simple. For the lead circle I'm moving it as follows on the movement of the mouse:

circle.x = event.stageX + 8.000000E-001 * ( circle.x - event.stageX );

circle.y = event.stageY + 8.000000E-001 * ( circle.y - event.stageY );

Then I'm moving the secondary circle as:

circle2.x = circle.x + 8.000000E-001 * ( circle2.x - circle.x );

circle2.y = circle.y + 8.000000E-001 * ( circle2.y - circle.y );

This works remarkably well, however, I want to be able to increase the distance between the two circles and enforce a minimum. If anyone can point me in the right direction I'd appreciate the assistance. Thanks.