Let f : R $\to$ R and g : R $\to$ R be defined as $$f(x) = \left\{ {\begin{matrix} {x + a,} & {x \lt 0} \\ {|x - 1|,} & {x \ge 0} \\ \end{matrix} } \right.$$ and $$g(x) = \left\{ {\begin{matrix} {x + 1,} & {x \lt 0} \\ {{{(x - 1)}^2} + b,} & {x \ge 0} \\ \end{matrix} } \right.$$, where a, b are non-negative real numbers. If (gof) (x) is continuous for all x $\in$ R, then a + b is equal to $\underline{\hspace{2cm}}$.