If the quadrature rule
$$
\int_{-1}^1 f(x) d x \approx f(\alpha)+\gamma f(\beta),
$$
where $\alpha, \beta$ and $\gamma$ are real constants, is exact for all polynomials of degree $\leq 3$, then $\gamma+3\left(\alpha^2+\beta^2\right)+\left(\alpha^3+\beta^3\right)$ is equal to
