gistfile1.txt

add_filter( 'the_content', 'prefix_insert_post_ads' );

function prefix_insert_post_ads( $content ) {

	if ( 'post' == get_post_type()  && is_single() && ! is_admin() ) {
		return prefix_insert_after_paragraph( 6, 1, $content );
	}
	
}

function prefix_insert_after_paragraph( $zone, $paragraph_id, $content ) {

	$contents = explode("</p>", $content);
	$p_count = 1;
	foreach($contents as $content)
	{
		$output .= $content; 

		if($p_count == $paragraph_id)
		{
		$output .= banner_zone($zone);
		}
		$output .=  "</p>";
		$p_count++;
	}
	return $output; 

}


function banner_zone($id){
	oiopub_banner_zone($id, 'center');

}