function nab(num)
{
	var i,nub=document.getElementById("tab").getElementsByTagName("li");
	for(i=0;i<nub.length;i++)
	{
		if(num==i)
		{
			document.getElementById("con"+i).className="block";
			nub[i].className="a";
		}
		else
		{
			document.getElementById("con"+i).className="none";		
			nub[i].className="b";
		}
	}
}