How to sell 1.2 protduct in hikashop?

-- url of the page with the problem -- : localhost
-- HikaShop version -- : 3.0.1
-- Joomla version -- : 3.7
-- PHP version -- : 5.6
-- Browser(s) name and version -- : firefox 57

Hi,
I want to know how customers can add 1.8 or 1.9856 product in their shopping cart?
I need to sell Digital Currencies, so customers need to add For Example(1.2 Ethereum), But in fact, customers can have 1 or 2 not the value between 1 and 2.
Please help me how to sell this much of product?