def lyambda_fact_bot(m_distrib, R, P_mol, F_mol, phi):
    """
    Calculates the the factor of masstransfer.
    Parameters
    ----------
    m_distrib : float
        The distribution coefficient, [dismensionless]
    R : float
        The reflux number, [dismensionless]
    P_mol : float
        The flow rate of distilliat, [kmol/s]
    F_mol : float
        The flow rate of feed, [kmol/s]
    phi : float
        The fraction of vapor at the feed point
    Returns
    -------
    lyambda_fact_bot : float
        The factor of masstransfer, [dismensionless]
    References
    ----------
    Дытнерский, стр.239 формула 6.35
    """      
    return m_distrib * (P_mol * (R + 1) - F_mol*phi) / (P_mol * R + F_mol * (1- phi))