// JavaScript Document

var name = "#dokurousagi";
var menuYloc = null;
$(document).ready(function(){

        menuYloc = parseInt($(name).css("top").substring(0,$(name).css("top").indexOf("px")))
       $(window).scroll(function () {
              offset = menuYloc+$(document).scrollTop()+"px";
              $(name).animate({top:offset},{duration:500,queue:false});
        });
});