I have list of numbers, and two destination blocks. I would like to drop number to target block, but keep only last dropped item. 

Here is the sample jsfiddle - [demo - which allows only one item drag](http://jsfiddle.net/jpatel/R2bFu/1/)

Code -

```
$(function() {
    $("ul.droptrue").sortable({
        connectWith: "ul",
    });

    $("ul.dropfalse").sortable({
        connectWith: "ul",
        dropOnEmpty: false
    });

    $("#sortable1, #sortable2, #sortable3").disableSelection();

    $("#sortable3,#sortable4").on("sortreceive", function(event, ui) {
        var $list = $(this);

        if ($list.children().length > 1) {
            $(ui.sender).sortable('cancel');

            //Move the existing one back to sortable1
            //Only keep the last moved element
        }
    });
});

```

In above example if user try to drag 2nd number to sortable3 or 4, it doesn't allow another number. The behavior I am expecting is if new number is dragged, the previous one should go back to sortable1 list (back to origin).

Thanks.