Let the functions f : R $ \to $ R and g : R $ \to $ R be defined as :$f(x) = \left\{ {\matrix{ {x + 2,} & {x < 0} \cr {{x^2},} & {x \ge 0} \cr } } \right.$ and $g(x) = \left\{ {\matrix{ {{x^3},} & {x < 1} \cr {3x - 2,} & {x \ge 1} \cr } } \right.$ Then, the number of points in R where (fog) (x) is NOT differentiable is equal to :