Smarty: Simple Prestashop aritmetic operation with variables

prestashop-aritmetic-var.tpl

  	{if $feature.id_feature == 16 }
			{assign var="shopPrice" value="`$feature.value`"}
	{/if}

	{if isset($shopPrice)}

		<div class="tienda-discount">

			{if $feature.id_feature == 16 }
				{assign var="shopPrice" value="`$feature.value`"}
			{/if}

			{assign var="save" value="`$shopPrice-$productPrice`"}

			Precio en tienda {$shopPrice}€ - Ahórrate {$save}€

		</div><!-- tienda-discount -->

	{/if}