Let $f(x)=\left\{\begin{array}{ll}\left|4 x^2-8 x+5\right|, & \text { if } 8 x^2-6 x+1 \geq 0 \\ {\left[4 x^2-8 x+5\right],} & \text { if } 8 x^2-6 x+1<0\end{array}\right.$ where $[\alpha]$ denotes the greatest integer less than or equal to $\alpha$. Then the number of points in $R$ where $f$ is not differentiable is $\_\_\_\_$ .