I am not understanding

Poss :

I created this small program. It should add to the cupboard some products. I get the following error:

TypeError: add_prod() missing 1 required positional argument: 'product'. 

Here is the code:

class Products:

    def __init__(self,nome):
        self.nome = nome

class Cupboard:

    def __init__(self):
        self.prod = []
    def add_prod(self, product):
        self.prod.append(product)

    def show(self):
        print(self.prod)


p1 = Products("Ajax")
p2 = Products("Barilla")

Cupboard.add_prod(p1)
Cupboard.add_prod(p2)

show()