\[a_{1} = 9;\ \ \]
\[a_{n} = 9n;\]
\[9n \leq 263\]
\[n \leq \frac{263}{9} \leq 29\frac{2}{9}.\]
\[n = 29.\]
\[a_{29} = 9 \cdot 29 = 261.\]
\[S_{29} = \frac{a_{1} + a_{29}}{2} \cdot 29 =\]
\[= \frac{9 + 261}{2} \cdot 29 = \frac{270}{2} \cdot 29 =\]
\[= 135 \cdot 29 = 3915.\]
\[Ответ:3915.\]