class memoized(object):
    '''Decorator. Caches a function's return value each time it is called.
       If called later with the same arguments, the cached value is returned
       (not reevaluated).
       '''
    def __init__(self, func):
        self.func = func
        self.cache = 0
    def __call__(self, *args):
        value = self.func(*args)
        self.cache += 1
        return value
    def quantos(self):
        return self.cache

@memoized
def fibonacci(n):
    if n in (0, 1):
        return n
    return fibonacci(n-1) + fibonacci(n-2)