Negative quantity value

Hikashop 2.2
Joomla 2.5.14

Is there a function that I can activate to get a negative Quantity value ?
I.e i have 5 pcs. of one product.
and I set the product Quantity to 5 pcs.

Then I sell 6 pcs of this products.....
Is it possible to make the Quantity to display -1 and I can still continue selling this product ?

That's not possible to handle negative quantities.
What you can do is start at 100 instead of 0. Thus, when you're at 99, it means that you sold out all the products and are missing one product already sold.