find second to last p

secondtolast.php

function ads_added_above_last_p($text) {
	
    if( is_single() ) {
		$ad_code5 = "<!-- /35404881/JOA_end_of_article_300x250_1 -->
<center><div id='div-gpt-ad-1466631079074-3' style='height:250px; width:300px;'>
<script type='text/javascript'>
googletag.cmd.push(function() { googletag.display('div-gpt-ad-1466631079074-3'); });
</script>
</div></center>";
        $last = strrpos($content, '</p>');
		if ($last === false) {
			return false;
		}
		$second_to_last = strrpos($content, '</p>', $last - strlen($content) - 2);

    return $content;
	}
}
add_filter('the_content', 'ads_added_above_last_p');