Revert

I have two divs, I am able to drag and drop into this divs.
But i want each div to contain only one draggable item. If one more
item is dragged into it, then tht should revert back.
Here is my code,
$(document).ready(function(){
$(".Drags").draggable({revert:'invalid',cursor: 'hand',opacity:
0.65});
$(".Dragged").droppable(
{
accept:".Drags"
})
$(".main").droppable({
accept:".Drags"})
});