static void Main(string[] args)
{
    DAG<string> dag = new DAG<string>();
    Vertex<string> vertex1 = new Vertex<string>("1");
    Vertex<string> vertex2 = new Vertex<string>("2");
    Vertex<string> vertex3 = new Vertex<string>("3");
    Vertex<string> vertex4 = new Vertex<string>("4");
    Vertex<string> vertex5 = new Vertex<string>("5");

    dag.AddVertex(vertex1);
    dag.AddVertex(vertex2);
    dag.AddVertex(vertex3);
    dag.AddVertex(vertex4);
    dag.AddVertex(vertex5);

    dag.TryAddEdge(vertex1, vertex3);
    dag.TryAddEdge(vertex2, vertex3);
    dag.TryAddEdge(vertex4, vertex5);
    dag.TryAddEdge(vertex3, vertex5);

    var result = dag.TopologicalSort();
    foreach (var item in result)
    {
        System.Console.WriteLine(item.Data);
    }
    // 1 2 4 3 5
}