import math


def t_dp(tdb, rh):
    """Calculates the dew point temperature.

    Parameters
    ----------
    tdb: float
        dry-bulb air temperature, [°C]
    rh: float
        relative humidity, [%]

    Returns
    -------
    t_dp: float
        dew point temperature, [°C]
    """

    c = 257.14
    b = 18.678
    d = 234.5

    gamma_m = math.log(rh / 100 * math.exp((b - tdb / d) * (tdb / (c + tdb))))

    return round(c * gamma_m / (b - gamma_m), 1)