Wordpress - Add CSS class to every fourth post

gistfile1.php

<?php if (have_posts()) : ?>
	<?php  
	// declare counter variable and assign it a value of 0
	$count = 0; 
	?>
  	<?php while (have_posts()) : the_post(); ?>
 
        	<?php if ($count % 4 == 3) { echo '<div class="post className">'; } else { echo '<div class="post>'; } ?>
          		<h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
          		<div class="entry">
          			<?php the_content(); ?>
          		</div>
          	</div><!-- .post -->
 
          	<?php 
          	// increment counter every time the loop is run
          	$count++;  
          	?>
          	
     	<?php endwhile; ?>
 <?php endif; ?>