Let $r_1$ and $r_2$ be the radii of the largest and smallest circles, respectively, which pass through the point $(-4,1)$ and having their centres on the circumference of the circle $x^2+y^2+2 x+4 y-4=0$. If $\frac{r_1}{r_2}=a+b \sqrt{2}$, then $a$ +b is equal to :
