def min_longitude(coordinates):
    """
    This function returns the minimum value of longitude
    of a list with tuples [(lat, lon), (lat, lon)].

    :param coordinates:     list
                            list with tuples. Each tuple
                            has coordinates float values.
                            [(lat, lon), (lat, lon)]
                            Ex:
                            [(-00.00, -00.00), (00.00, 00.00)]

    :return:                float
                            minimum longitude value
    """
    min_lon = min(coordinates, key=lambda t: t[1])[1]
    return min_lon