I want adding string @ in every second comma
<p>I want to change <code>'a,b,c,d,e,f,g,e'</code> to  <code>'a,b@c,d@e,f@g,e'</code>.  </p>

<p>Input:</p>

<pre><code>'a,b,c,d,e,f,g,e'
</code></pre>

<p>Output:</p>

<pre><code>'a,b@c,d@e,f@g,e'
</code></pre>

<p>Is it possible?</p>