Let
\( A =
\begin{bmatrix}
x & y & z \\
y & z & x \\
z & x & y
\end{bmatrix} \),
where \( x, y \) and \( z \) are real numbers such that
\( x + y + z > 0 \) and \( xyz = 2 \).
If \( A^2 = I_3 \), then the value of
\( x^3 + y^3 + z^3 \) is __________.