Calculate [D+] and [OD]- for pure(neutral) D2O at 20 degrees celsius.?

Deuterium oxide(D20, where D is deuterium, the hydrugen-2 isotope) has an ion product constant, Kw, of 8.9 x 10^-16 at 20 degrees celsius. Calculate [D+] and [OD]- for pure(neutral) D2O at this temperature.