function show_submenu(num)
{	
	if (document.getElementById("sub_menu"+num).style.display == "none")
	{
		document.getElementById("sub_menu"+num).style.display = "block";
	}
	else if (document.getElementById("sub_menu"+num).style.display == "block")
	{ 
		document.getElementById("sub_menu"+num).style.display = "none";
	} 		
}