How many integer solutions are there to the inequality $x_1 + x_2 + x_3 \leq 17$ if we require that $x_1 \geq 1$, $x_2 \geq 2$, $x_3 \geq 3$?
(Probability) How many integer solutions are there to the inequality $x_1 + x_2 + x_3 \le 17$