Bipartite Graphs and Matchings · Medium problem

A network has a main line of routers $1\text{-}2\text{-}3\text{-}4\text{-}5\text{-}6\text{-}7$ (a path), with one extra router $8$ attached directly to router $4$. What is the size of a maximum matching (pairs of routers linked directly, each router in at most one pair)?