import math


def normalize_radian(rad: float):
    """Return the normalized azimuth

    Arguments:
        azimuth {float} -- azimuth

    >>> round(normalize_radian(3.14), 6)
    3.14
    >>> round(normalize_radian(-3.14), 6)
    -3.14
    >>> round(normalize_radian(3.15), 6)
    -3.133185
    >>> round(normalize_radian(-3.15), 6)
    3.133185
    """

    v = math.fmod(rad, 2 * math.pi)
    if -math.pi < v and v <= math.pi:
        return v
    else:
        return v - math.copysign(2 * math.pi, v)