The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.5807\\[1 em]x_2 &= 1.7221\\[1 em]x_3 &= -0.6514+0.7587i\\[1 em]x_4 &= -0.6514-0.7587i \end{aligned} $$Polynomial $ -x^4+x^3+x^2+x-1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.