Need help with adding a class to a specific item in a loop

In my design, I have 3 col to display the latest from a blog. I ran the wordpress loop to return 3 results and now I need to add a class to the last (or 3rd) div in the loops return. This is what I have, any help would be much appreciated.

<script type="text/javascript">
	$(".blog:last").addClass('last');			
</script>
<?php query_posts('post_per_page=3'); ?>
<?php if(have_posts()) : while(have_posts()) : the_post(); ?>

<div class="three-even blog">
     content goes here......
</div><!--END three-even last-->
    
<?php endwhile; ?>
    
<?php endif; ?>

Code (markup):