# not recursive soln.
# lengths = {}
# def size(n):
    # count = 0
    # while n > 1:
        # if n in lengths:
            # return count + lengths[n]
        # count += 1
# 
        # if n % 2 == 0:
            # n = n/2
        # else:
            # n = 3*n + 1
    # return count

# simple cache
def cache(func):
    results = {}
    def f(arg):
        if arg not in results:
            results[arg] = func(arg)
        return results[arg]
    return f

# what is py max recursion depth?
@cache
def r_size(n):
    if n <= 1:
        return 1
    elif n % 2 == 0:
        return 1 + r_size(n/2)
    else:
        return 1 + r_size(3*n + 1)


def seqTo(num):
    for n in range(num):
        s = r_size(n)
        yield s, n

# print r_size(13)
if __name__ == '__main__': print max(seqTo(1000000))