A rabbit population grows according to the recurrence $R(n) = R(n-1) + R(n-2) - R(n-3)$ (births, survival, and a predation term) with $R(0) = 1, R(1) = 1, R(2) = 1$. The characteristic polynomial is $r^3 - r^2 - r + 1 = 0$. Which of the following is a root?