Brake not to drag on sortable

This week I got help from Lúcio Rubens with a question, he helped me with this code, to get the IDs of the clicked elements.

Now on top of this same code, I need to lock a UL so it will not allow more elements to be removed,

This is the working example, JSFiddle.

$(".items").sortable({
    connectWith: ".items",
    receive: function(event, ui) {
        var id_origem = ui.sender.attr("id"),
            id_clicado = ui.item.attr("id"),
            id_destino = $(this).attr("id");
    }
});