[填空题]
The plane $\Pi$ has the Cartesian equation x+y+3 z=5 . The line L has the vector equation $\mathbf{r}=\left(\begin{array}{c}2 \\ 3 \\ -1\end{array}\right)+\lambda\left(\begin{array}{c}-1 \\ 1 \\ p\end{array}\right), \lambda, p \in \mathbb{R}$ . The acute angle between the line L and the plane $\Pi $ is $60^{\circ}$ . Find the possible values of p . ±
