User::getAdminId

static function getAdminId()
{
	global $USER;

	$id = static::getId();
	if($id && $USER->isAdmin())
	{
		return $id;
	}

	static $admin;

	if($admin === null)
	{
		$user = CUser::GetList(
			'id',
			'asc',
			array('GROUPS_ID' => array(1), 'ACTIVE' => 'Y'),
			array('FIELDS' => array('ID'), 'NAV_PARAMS' => array('nTopCount' => 1))
		)->fetch();

		if (is_array($user) && intval($user['ID']))
		{
			$admin = intval($user['ID']);
		}
	}

	return $admin === null ? 0 : $admin;
}