For an ecosystem undergoing succession, the change in species diversity D over time is given by the differential equation $$\frac{dD}{dt}= k*(S_{max}- D)$$, with the solution $$D(t)= S_{max} - (S_{max}- D(0))*e^{-k*t}$$. If the initial diversity is 10 species, the maximum diversity $$S_{max}$$ is 50 species, and k = 0.05 per year, what is the expected species diversity after 20 years?