\[\boxed{\mathbf{504}.}\]
\[x = \sqrt[3]{- \frac{b}{2} + \sqrt{\frac{b^{2}}{4} + \frac{a^{3}}{27}}} +\]
\[+ \sqrt[3]{- \frac{b}{2} - \sqrt{\frac{b^{2}}{4} + \frac{a^{3}}{27}}}\]
\[Пусть\ y = \sqrt[3]{- \frac{b}{2} + \sqrt{\frac{b^{2}}{4} + \frac{a^{3}}{27}}};\ \]
\[\ z = \sqrt[3]{- \frac{b}{2} - \sqrt{\frac{b^{2}}{4} + \frac{a^{3}}{27}}};\]
\[y^{3} + z^{3} = - \frac{b}{2} + \sqrt{\frac{b^{2}}{4} + \frac{a^{3}}{27}} - \frac{b}{2} -\]
\[- \sqrt{\frac{b^{2}}{4} + \frac{a^{3}}{27}} = - b.\]
\[x^{3} = (y + z)^{3} = y^{3} + 3y^{2}z +\]
\[+ 3yz^{2} + z^{3} = y^{3} + z^{3} +\]
\[+ 3yz(y + z) =\]
\[= - b + 3 \cdot \left( - \frac{a}{3} \right)x = - b - ax\]
\[x^{3} + ax + b = - b - ax +\]
\[+ ax + b = 0.\]
\[Ответ:0.\]