Calling a base class's classmethod in Python

Consider the following code:

class Base(object):

    @classmethod
    def do(cls, a):
        print cls, a

class Derived(Base):

    @classmethod
    def do(cls, a):
        print 'In derived!'
        # Base.do(cls, a) -- can't pass `cls`
        Base.do(a)

if __name__ == '__main__':
    d = Derived()
    d.do('hello')

> $ python play.py  
> In derived! 
> <class '__main__.Base'> msg

From Derived.do, how do I call Base.do?

I would normally use super or even the base class name directly if this is a normal object method, but apparently I can't find a way to call the classmethod in the base class.

In the above example, Base.do(a) prints Base class instead of Derived class.