Directed Graphs and Network Flows · Medium problem

A digraph has vertices $1,\dots,6$ and arcs $1\to2$, $1\to3$, $2\to4$, $3\to4$, $4\to5$, $3\to5$, $5\to6$, $2\to6$. What is the length of the shortest directed walk from $1$ to $6$ that passes through vertex $5$?