Are you referring to no of items in the current cart or also referring to the fact if it is a returning customer has already purchased that product before?
I am assuming you are referring to the current basket/cart. In that case I think you need something like this
Since your condition is >=1 it means you have to just check if the number of iems in the cart is at least 1
You can also refer to this article which covers advanced cart scenarios with examples. This article was written by Jan from Kentico team.