Buy 3 products of a category and get them for €159. How can this be configured in magento M2

[Loginname]

hi

magento 2.2.2.

If customer buys 3 products from a certain cateogry he will get them for only €159. I wonder how this can be configured

key info:

* customer can buy 3 items of the same product and then get them for $159

* customer can buy 3 different products from the same category and get them for $159

* it allies to all customers

* all my websites

how can I apply this discount?

We are selling various products and now we want to give discount