Automatically Return Checkbox State to Normal Once 'X' Number of Checkboxes have been Checked

Hello,

I have a dozen statements each with a checkbox. I want the user to select three of those statements by checking the corresponding checkbox. So far so easy...

But then...

There can only be three boxes checked at a time so if the user selects a fourth statement one of the currently checked checkboxes should return to its normal unchecked state (ideally the one that has been checked the longest).

Any ideas?