Adding Adsense Code

I wanted to add adsense Ads between every 3 blog grids using your Post Grid element in Visual Composer. Which file and after what code should I place the adsense code? See the screenshot below: http://i.imgur.com/5GgP7Qa.jpg

I was given the following code to be placed in the index.php file of the theme, but that is only showing on the blog page selected in the Settings>Reading and not between the grids.

======================================
<div class=”westarticle”>
<?php $postnum++; if($postnum%2 == 0) { ?>
<script async src=”//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js”></script>
<!– New landing 2 –>
<ins class=”adsbygoogle”
style=”display:inline-block;width:325px;height:405px”
data-ad-client=”ca-pub-1829550496124713″
data-ad-slot=”3068513484″></ins>
<script>
(adsbygoogle = window.adsbygoogle || []).push({});
</script>
<?php } ?>
</div>
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Please help, its urgent!