Graph Algorithms · Challenge problem

A directed graph on vertices $1$–$6$ has edges $1\to2, 2\to3, 3\to1, 3\to4, 4\to5, 5\to3, 5\to6$. This digraph has directed cycles, so it has no topological order. What is the fewest edges that must be removed so that the remaining digraph IS a DAG?