jQuery(function($) {
    var pos;
    var w;
    var h;
    var ad;
    var offset;
    var load_comp;
    
    $(window).load(function () {
    	load_comp = 1;
    });
	$(window).scroll(function () {
		if(!load_comp){
			return;
		}
		if($('#left').height() >= $('#center').height()){
			return;
		}
		ad = $('#slide_ad');
    	offset = ad.offset();
		if($(window).scrollTop() > offset.top) {
    		if(!pos){
    			pos = offset.top;
    			w = ad.width();
    			h = ad.height();
    		}
    		ad.addClass('fixed');
    		ad.css({
    		    width:w,
    		    height:h
    		});

  		} else {
  			if(!pos){
  				return;
  			}
  			if(pos > offset.top){
    			ad.removeClass('fixed');
    			pos = undefined;
    		}
  		}
	});
});