import math


def normalize_angle(angle):
    """
    Normalizes specified angle (in radians) to 0 to 2*PI
    :param angle: specified angle (in radians) 
    :return: normalized angle
    """
    res = angle
    while res > math.pi:
        res -= 2.0 * math.pi
    while res <= -math.pi:
        res += 2.0 * math.pi

    return res