def mcd(a: int,
        b: int) -> int:
    """This function returns the greatest common divisor from a and b.

    Args:
        a (int): dividend.
        b (int): divider.
    Returns:
        int: the GCD from a and b.
    """
    if a % b == 0:
        return b

    return mcd(b, a % b)