\textbf{20 --} What is the minimum distance from points on the curve $y = \sqrt{x - [x^2]}$ to the line $x - y + 2 = 0$?
\medskip
(1) $\dfrac{\sqrt{5}}{5}$ \hfill (2) $\dfrac{3\sqrt{5}}{8}$ \hfill (3) $\dfrac{\sqrt{5}}{10}$ \hfill (4) $\dfrac{3\sqrt{5}}{10}$
\bigskip