Let $f: R \rightarrow R$ be defined as
$$
f(x)=\left\{\begin{array}{cc}
2 \sin \left(-\frac{\pi x}{2}\right), & \text { if } x<-1 \\
\left|a x^2+x+b\right|, & \text { if }-1 \leq x \leq 1 \\
\sin (\pi x) & \text { if } x>1
\end{array}\right.
$$
If $f(x)$ is continuous on $R$, then $a+b$ equals :
