The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.6924+0.3182i\\[1 em]x_2 &= -0.6924-0.3182i\\[1 em]x_3 &= 1.1924+0.5479i\\[1 em]x_4 &= 1.1924-0.5479i \end{aligned} $$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.