def michea_m(num_types, freq_spectrum):
    """Calculate Michéa’s M (1969, 1971).

    Used formula:
        .. math::
            M = rac{V}{D}

    Parameters:
        num_types (int): Absolute number of types.
        freq_spectrum (dict): Counted occurring frequencies.
    """
    return num_types / freq_spectrum[2]
