If checkbox :checked more than 3 last one should unchecked

I have 6 input[type="checkbox"].

User can select only 3 checkbox at a time.
If user selects the 4th checkbox then last checked(3rd checkbox) should unchecked.

Find image attachment for better understanding.

Meanwhile, if User selects 5th last selected (4th) should deselect.

As, I'm not able to create this logic so that I made fiddle demo in which if selected more than 3. The current one is not getting selected.

Find fiddle demo

$('input[type=checkbox]').click(function(e) {
var num_checked = $("input[type=checkbox]:checked").length;
if (num_checked > 3) { 
  $(e.target).prop('checked', false);
}
});