Let $f:\mathbf{R}\rightarrow\mathbf{R}$ be defined as $ f(x)= \begin{cases} \dfrac{a - b\cos 2x}{x^2}, & x < 0, \\[6pt] x^2 + cx + 2, & 0 \le x \le 1, \\[6pt] 2x + 1, & x > 1. \end{cases} $ If $f$ is continuous everywhere in $\mathbf{R}$ and $m$ is the number of points where $f$ is **not differentiable**, then $m + a + b + c$ equals :