\[\boxed{\text{617\ (617).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[x_{1} = 3,\ \ x_{2} = 5,\ \ d = x_{2} - x_{1} = 2:\ \]
\[S_{n} = \frac{2x_{1} + d(n - 1)}{2} \cdot n = \frac{6 + 2 \cdot (n - 1)}{2} \cdot n = (3 + n - 1) \cdot n =\]
\[= (n + 2) \cdot n = n^{2} + 2n \leq 120;\]
\[n^{2} + 2n - 120 \leq 0\]
\[D = 1 + 120 = 121\]
\[так\ как\ n > 0 \Longrightarrow n = - 1 + 11 = 10.\]
\[Ответ:10\ членов.\]