1. The problem statement, all variables and given/known data

Find a functionf: [-1,1] --->Rsuch that f satisfies the following properties:

a) f is continuous

b) f is restricted to (-1,1) is differentiable

c) its derivative f' is not differentiable on (-1,1)

2. Relevant equations

3. The attempt at a solution

I kinda think that the mean value theorem and Theorem 2 of the fundamentals f(x)dx = F(b)-F(a) got some link but I can't seem to get it. I do understand that for f'' not to exist, x should be undefined on the (-1,1). Please help.