import math


def two_divider(num):
    """Solution to exercise P-1.30.

    Write a Python program that can take a positive integer greater than 2
    as input and write out the number of times one must repeatedly divide
    this number by 2 before getting a value less than 2.
    """
    if not isinstance(num, int) or (num < 3):
        raise ValueError
    return int(math.log(num, 2))