Insert Ads inside Post Content

gistfile1.php

<?php
add_filter('the_content', 'rr_add_ad_inside_post');
function rr_add_ad_inside_post($content) {
   if ( is_single() ) {
       	$paragraphAfter= 3; //display after the first paragraph
        $content = explode("", $content);
        for ($i = 0; $i <count ($content); $i++ ) {
		if ($i == $paragraphAfter) { ?>
		 <p class="alignleft">
			<script type="text/javascript"><!--
			google_ad_client = "pub-xxxxxxxxxx";
			/* 250x250, created 9/10/11 */
			google_ad_slot = "xxxxxxxxx";
			google_ad_width = 250;
			google_ad_height = 250;
			//-->
			</script>
			<script type="text/javascript"
			src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
			</script>
		</p>
		<?php }
		echo $content[$i] . "</p>";
		} 
	}
}
?>