function getYOffset() {
    var pageY;
    if(typeof(window.pageYOffset)=='number') {
       pageY=window.pageYOffset;
    }
    else {
       pageY=document.documentElement.scrollTop;
    }
    return pageY;
}

function scroll() {
	$('downloadbt').show();
	//console.log($('downloadbt'));
	if (getYOffset() > xHeight('home_menu') + xPageY('home_menu')){
	$('downloadbt').style.marginTop = getYOffset() - xPageY('home_menu') + 'px';
	}else if(getYOffset() < xHeight('home_menu') + xPageY('home_menu')){
	$('downloadbt').style.marginTop = xHeight('home_menu') + 'px';
	}
	
}

$('downloadbt').hide();

window.onscroll = scroll;