dCartes

Hello I have a problem with Prestashop. I hope somebody can help me solving it. There is situation when only one item left. One buyer, we call buyer A, has already added it to the cart. When another buyer want to add that item to their cart, they will immediately get a notification that product out of stock. If the buyer A cancel or remove the item from his/her cart, then the item will be available again for another buyer. Please help me get this thing done. Thank you for your help and time