adding adsense code to index.php

I am using WP ‘Twenty Eleven’ theme and I want to display adsense ad on my main/home pgae just below the page menu. In another theme, I was able to achieve that by inserting the code into the index.php, just before <?php if (have_posts()) : ?>
I am trying in the same area of this theme but it is not working…the code looks something like:

[code moderated - please follow the forum guidelines for posting code]

Do I need to add anything around (before and after) the codes I am inserting? like <?php..?
Please advise.
Thanks.

PS: My web site is http://www.theindiansabroad.com if you need to view it.