$\begin{aligned} r_{0}+r_{0} r_{1}+r_{0} r_{1} r_{2}+\cdots+r_{0} r_{1} r_{2} \cdots r_{n}=\\ \frac{r_0}{1-\frac{r_1}{1+r_2-\frac{\ddots}{\ddots\frac{r_{n-1}}{1+r_{n-1}-\frac{r_n}{1+r_n}}}}}= \end{aligned}$