// Decide if id is Odd or even and do
if($contact_id % 2){
	// If odd add this tag
    $contact = array(
		"email"		=> $contact_email,
		'tags' 		=> 'hr-split-a',
	);
	$contact_sync = $ac->api("contact/sync", $contact); // sync with AC
}else{
	// If even add this tag
    $contact = array(
		"email"		=> $contact_email,
		'tags' 		=> 'hr-split-b',
	);
	$contact_sync = $ac->api("contact/sync", $contact); // sync with AC
}