Display subpages with child of

Hi!
I’m trying to display the subpages on a page and I use the code below. It works perfectly, but I need it changed a little.

<?php
	$page_ids = array();
	$subpages = get_pages('depth=4&child_of='.$post->ID.'&sort_column=post_title');
	if($subpages)foreach($subpages as $subpage) { $page_ids[] = $subpage->ID; } 

	$subpages = new WP_Query( array(
		'post_type' => 'page',
		'post__in' => $page_ids,
		'orderby' => 'title',
		'paged' => get_query_var('paged')
		));
	$count = 0;
	if($page_ids && $subpages->have_posts()) : ?>
<ul class="product_list">
<?php while($subpages->have_posts()) : $subpages->the_post(); ?>

<li>
        <div class="product_layout">
  <div class="thumb1"><a href="<?php echo get_page_link($post->ID) ?>"><?php echo get_the_post_thumbnail($post->ID, 'thumbnail'); ?></a>
  <a href="<?php echo get_page_link($post->ID) ?>" title="<?php echo $post->post_title ?>"><?php $thetitle=$post->post_title; $getlength = strlen($thetitle);
$thelength = 18;
echo substr($thetitle, 0, $thelength);
if ($getlength > $thelength) echo "..."; ?></a></div>
    <div class="bottom"></div> 

</li>

	<?php endwhile; ?>
 </ul>

At some point I have Page1 with the SubPage1 whom has a SubSubPage1 with a SubSubSubPage1 and the code displays all of them,
I want it to show me only the SubSubSubPage1 and I tried using
depth but it doesn’t work. I used it like that:

<?php
	$page_ids = array();
	$subpages = get_pages('depth=4&child_of='.$post->ID.'&sort_column=post_title');
	if($subpages)foreach($subpages as $subpage) { $page_ids[] = $subpage->ID; } 

	$subpages = new WP_Query( array(
		'post_type' => 'page',
		'post__in' => $page_ids,
		'orderby' => 'title',
		'paged' => get_query_var('paged')
		));
	$count = 0;
	if($page_ids && $subpages->have_posts()) : ?>

Can someone help me?