php preg_match get numbers between two strings

Hi I'm starting to learn php regex and have the following problem: I need to extract the numbers inside $string. The regex I use returns "NULL".

$string = 'Clasificación</a> (2194)  </li>';
$regex = '/Clasificación</a>((.*?))</li>/';
preg_match($regex , $string, $match);
var_dump($match);

Thanks in advance.