def euklid_dist(coord1, coord2):
    """
    Return euklidian distance between atoms coord1 and coord2.
    """
    xd2 = (coord1[0]-coord2[0]) ** 2
    yd2 = (coord1[1]-coord2[1]) ** 2
    zd2 = (coord1[2]-coord2[2]) ** 2
    return (xd2 + yd2 + zd2)**0.5