function navigation(nav){
	navbar=document.getElementById("main_menu").getElementsByTagName('li');
	for (i=0;navbar[i];i++){
		if (navbar[i].id=="nav"+nav)
			navbar[i].className="main_active";
		else
			if (navbar[i].id=="nav7")
				navbar[i].className='end';
			else
				navbar[i].className='';
			
	}
	
	navbar=document.getElementById("sub_menu").getElementsByTagName('ul');
	for (i=0;navbar[i];i++){
		if (navbar[i].id=="sub"+nav)
			navbar[i].style.display="block";
		else
			navbar[i].style.display="none";
	}
}