$allowed_ids = array(1=>"1.php",2=>"2.php",3=>"3.php");
$ID = intval($_GET['ID']);
$page = "";
if(array_key_exists($ID,$allowed_ids))
{
        $page = $allowed_ids[$ID];
        include ('header.php');
        include ($page);
        include ('footer.php');
}
else
{
        include ('noid.php');
}