#separability

Four one-dimensional training points are labelled $x = 0$: $+1$, $x = 1$: $-1$, $x = 2$: $+1$, $x = 3$: $-1$. An SVM uses the polynomial kernel $K(x, x') = (1 + x x')^p$. What is the smallest degree $p$ for which the points are separable?