Hey guys, so i have the following:

$\displaystyle f''(a) = \lim_{h \to 0}\frac{f(a+h)-2f(a)+f(a-h)}{h^2}$

and I'm trying to figure out a function that works for that limit, but doesn't have a second derivative at $\displaystyle a$... been scratching my head over this one for a while lol thanks!