How can I place ad code after every 5 activities in BuddyPress activity loop?

Here’s where I would start:

<?php $count = 0; ?>
<?php while ( bp_activities() ) : bp_the_activity();?>
  <?php
    bp_get_template_part( 'activity/entry' );
    $count++;
    if ( $count % 5 == 0 ) {
      the_ad(3860);
    }
  ?>
<?php endwhile; ?>