Adding javascript code

Hi
I need to install a chat demo in the site, but when I try to insert the javascript code in “Custom Javascript”, the system show me alerts. The code was given to me by the company (zopim). The newspaper theme panel say “Please do not include the <script> </ script>”, and if I delete this, the system shows me alert messages. I do not know how to enter it. the code is

<!–Start of Zendesk Chat Script–>
<script type=”text/javascript”>
window.$zopim||(function(d,s){var z=$zopim=function(c){
z._.push(c)},$=z.s=
d.createElement(s),e=d.getElementsByTagName(s)[0];z.set=function(o){z.set.
_.push(o)};z._=[];z.set._=[];$.async=!0;$.setAttribute(‘charset’,’utf-8′);
$.src=’https://v2.zopim.com/?5UGUoBISPPvytCAgmH44AniqGGti4trK&#8217;;z.t=+new Date;$.
type=’text/javascript’;e.parentNode.insertBefore($,e)})(document,’script’);
</script>
<!–End of Zendesk Chat Script–>

Thank!

Thanks. Finally the script could be inserted in footer and no in head. I don’t know why, but now works.
Thanks again.