$(document).ready(function(){
var $menu = $('#left');
function setMenu(){
if($menu.outerHeight() < $(window).height()){
$menu.css('position', 'fixed');
} else {
$menu.css('position', 'relative');
}
}
setMenu();
$(window).scroll(function(){
setMenu();
});
$(window).resize(function(){
setMenu();
});
});