def greatest_common_divisor(a, b):
    """
    Get the greatest common divisor of two numbers

    @param a: First number.
    @type  a: C{int}

    @param b: Second number.
    @type  b: C{int}

    @return: Greatest common divisor.
    @rtype:  C{int}
    """
    while b != 0:
        t = b
        b = a % b
        a = t
    return a
