About statistics of periods of continued fractions of quadratic irrationalities

In this paper we answer certain questions posed by V.I. Arnold, namely, we study periods of continued fractions for solutions of quadratic equations in the form $x^2+p x=q$ with integer $p$ and $q$, $p^2+q^2\le R^2$. Our results concern the average sum of period elements and Gauss--Kuzmin statistics as $R\to\infty$.