$(document).ready(function() {
    var p = $('#navcontainer>p'), nav = $('#nav');
    p.css({cursor:'pointer'}).click(function(){
        if ( false == p.is('.opened') ) {
            p.addClass('opened');
            nav.slideToggle(500);
        }
        else nav.slideToggle(500, function(){ p.removeClass('opened'); });
    });
});