Directed Graphs and Network Flows · Easy 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 (number of arcs) of the shortest directed path from vertex $1$ to vertex $6$?