6. Let $0 \leqslant x_{i} \leqslant 1(i=1,2, \cdots, 5)$. Then
$$
\begin{array}{l}
\left|x_{1}-x_{2}\right|^{3}+\left|x_{2}-x_{3}\right|^{3}+\left|x_{3}-x_{4}\right|^{3}+ \\
\left|x_{4}-x_{5}\right|^{3}+\left|x_{5}-x_{1}\right|^{3}
\end{array}
$$

The maximum value is . $\qquad$