A group of 9 students, $s_1, s_2, \ldots, s_9$, is to be divided to form three teams $\mathrm{X}, \mathrm{Y}$ and, Z of sizes 2,3 , and 4 , respectively. Suppose that $s_1$ cannot be selected for the team X , and $s_2$ cannot be selected for the team Y . Then the number of ways to form such teams, is $\_\_\_\_$