How to take integer from an string value which is stored in a method/function?

In buddypress plugin subject is printed using this code

<?php bp_the_thread_subject(); ?>

at my end this function/method is printing result like Hello world: 1236 . I want to take only integer value from this. But when i am applying anything to this function/method, it is getting zero result. How to do that ?

via Chebli Mohamed