Adicionar anuncio meio da postagem single.php automatico

$paragraphAfter[1] = '<div>AFTER FIRST</div>'; //display after the first paragraph
$paragraphAfter[3] = '<div>AFTER THIRD</div>'; //display after the third paragraph
$paragraphAfter[5] = '<div>AFTER FIFtH</div>'; //display after the fifth paragraph

$content = apply_filters( 'the_content', get_the_content() );
$content = explode("</p>", $content);
$count = count($content);
for ($i = 0; $i < $count; $i++ ) {
    if ( array_key_exists($i, $paragraphAfter) ) {
        echo $paragraphAfter[$i];
    }
    echo $content[$i] . "</p>";
}