8. Let the graph of the parabola $y=a x^{2}+b x+c$ pass through the points $A(-1,-3) 、 B(4,2) 、 C(0,2)$. Let $P$ be a moving point on the axis of symmetry of the parabola. If $P A+P C$ takes the minimum value when the coordinates of point $P$ are $(m, n)$, then $n=$ $\qquad$