Subtracting two variables in Phpfox template

How can I subtract two variables in template?

For example,

{foreach from=$aArray key=sKey item=sItem name=arr}
    <p>{$aArray|count} - {$phpfox.iteration.arr}</p>
{/foreach}

I did the following solutions, however they didn't work:

First Solution:

{foreach from=$aArray key=sKey item=sItem name=name}
     {assign var="iCurrent" value=count($aArray)-$phpfox.iteration.arr}
     <p>{$iCurrent}</p>
{/foreach}

Second Solution:

{foreach from=$aArray key=sKey item=sItem name=name}
     {assign var="iCurrent" value=(int)count($aArray)-(int)$phpfox.iteration.arr}
     <p>{$iCurrent}</p>
{/foreach}

Thanks.

Can you try this

{foreach from=$aArray key=sKey item=sItem name=name}
     <p>
         <?php echo (count($this->_aVars['aArray']) - $this->_aVars['phpfox']['iteration']['arr']); ?>
     </p>
{/foreach}