[jQuery] droppable limit

[jQuery] droppable limit


Hi
i use for drag and drop this easy code
$(function() {
        $(".ui-draggable").draggable({ revert: 'invalid' });
        $(".ui-droppable").droppable({
            accept: '.ui-draggable',
            drop: function(event, ui) {
                $(this).addClass('red');
            },
            out: function(event, ui) {
                $(this).removeClass('red');
            }
        });
});
i have some boxes and some containers. i want add ONLY one box to one
container. How can i limit number of boxex that will container
accept? thanks for every help.