For 1s-orbital of hydrogen atom radial wave function is given as: 
$\mathrm{R}\left(\mathrm{r}\right)=\frac{1}{\sqrt{\mathrm{\pi }}}{\left(\frac{1}{{\mathrm{a}}_0}\right)}^{3/2}{\mathrm{e}}^{-\mathrm{r}/{\mathrm{a}}_0}(\mathrm{where} {\mathrm{a}}_0=0.529\mathrm{\hspace{0.17em}}\stackrel{\mathrm{o}}{\mathrm{A})}$
The ratio of radial probability density of finding electron at $\mathrm{r}={\mathrm{a}}_0$ to the radial probability density of finding electron at the nucleus is given as $(\mathrm{x}\cdot {\mathrm{e}}^{-\mathrm{y}})$. Calculate the value of  (x + y).