For the elementary reactions in series
$$\mathrm{A} \stackrel{k_{1}}{\longrightarrow} \mathrm{R} \stackrel{k_{2}}{\longrightarrow} \mathrm{S}, \quad k_{1}=k_{2}, \quad \text { at } t=0 \quad\left\{\begin{array}{c}
C_{\mathrm{A}}=C_{\mathrm{A} 0} \\
C_{\mathrm{R} 0}=C_{\mathrm{S} 0}=0
\end{array}\right.$$
find the maximum concentration of $\mathrm{R}$ and when it is reached.