Nvaigation on Sub-Sub Pages

Hello I came across this problem and hope to get help here:

If I want to show the navigation of the parent pages on a SubPage I use this:

<?php
if($post->post_parent)
$children = wp_list_pages("title_li=&child_of=".$post->post_parent."&sort_column=menu_order&show_date=modified&date_format=$date_format&echo=0");
else
$children = wp_list_pages("title_li=&child_of=".$post->ID."&sort_column=menu_order&show_date=modified&date_format=$date_format&echo=0");
if ($children) { ?>
<ul  class="menu">
<?php echo $children; ?>
</ul>
<?php } ?>

However, if I go to a sub page of a sub-page, I only get the navigation of the pages on the same level, but not their parent-level.

For Example:

I have this structure

Page0
Page1
Page2
Subpage
Subsubpage01
Subsubpage02

With the code above I get on the page-level and subpagelevel the whole navigation, but on the Subsubpage I can see only subsubpage01 and subsubpage02

How do I get the full navigation here?