Graph Coloring · Hard problem

Let $C_7$ be the $7$-cycle on vertices $1,\ldots,7$ with edges $12,23,34,45,56,67,71$. Let $G$ be the COMPLEMENT of $C_7$: two vertices are adjacent in $G$ exactly when they are NOT adjacent in $C_7$ (and are not the same vertex). What is $\chi(G)$?