Limit, Continuity and Differentiability: JEE Main 2023 Mathematics question

Let $a \in \mathbb{Z}$ and $[\mathrm{t}]$ be the greatest integer $\leq \mathrm{t}$. Then the number of points, where the function $f(x)=[a+13 \sin x], x \in(0, \pi)$ is not differentiable, is __________.