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 :