def cache(f):
    """
    simple hash cache.
    Makes key by:
    ''.join(str(a) for a in args)
    Will choke on kwargs for the moment.
    """
    cache_data = {}
    def _(*args):
        key = ''.join(str(a) for a in args)
        try:
            print len(cache_data)
            return cache_data[key]
        except KeyError:
            res = f(*args)
            cache_data[key] = res
            return res
    return _

# @cache

primes = {}

def isPrime(num):

    n = 2
    while n < num:
        if num % n == 0:
            primes[n] = False
            return False
        n += 1

    primes[num] = True
    return True


# greatest prime factor
def gpf(n):
    i = 2
    while 1:
        # print i/float(n)
        if (n % i == 0):
            print i, n/i, isPrime(i), isPrime(n/i)
            if (isPrime(n/i)):
                return i
        i += 1

if __name__ == '__main__':
    print gpf(317584931803);