The domain of $\operatorname { Sin } ^ { - 1 } \left( \frac { 1 } { x ^ { 2 } - 2 x - 1 } \right)$ is $( - \infty , \alpha ] \cup [ \beta , \gamma ] \cup [ \delta , \infty )$. The value of $\alpha + \beta + \gamma + \delta$ is equal to: