class Edge
    {
        public readonly Node First;
        public readonly Node Second;
        public Edge(Node first,Node second)
        {
            First = first;
            Second = second;
        }

        public bool IsIncident(Node node)
        {
            return node == First || node == Second;
        }
        public Node OtherNode (Node node)
        {
            if (First == node) return Second;
            else if (Second == node) return First;
            else throw new ArgumentException();
        }
    }
/*****************************************************/

class Graph
    {
        private Node[] nodes;
        public Graph(int nodesCount)
        {
            nodes = Enumerable
                .Range(0, nodesCount)
                .Select(z => new Node(z))
                .ToArray();
        }

        public Node this[int i]
        {
            get { return nodes[i]; }
        }

        public IEnumerable<Node> Nodes
        {
            get
            {
                foreach (var node in nodes)
                {
                    yield return node;
                }
            }
        }
        
        public IEnumerable <Edge> Edges
        {
            get
            {
                return Nodes.SelectMany(z => z.incidentEdges).Distinct();
            }
        }

        public static Graph MakeGraph(params int[] incidentNodes)
        {
            var graph = new Graph(incidentNodes.Max() + 1);
            for (int i = 0; i < incidentNodes.Length - 1; i += 2)
                graph.Connect(incidentNodes[i], incidentNodes[i + 1]);
            return graph;
        }

        public void Connect(int v1,int v2)
        {
            nodes[v1].Connect(nodes[v2]);
        }
    }
/*****************************************************/
class Node
    {
        private readonly List<Edge> IncidentEdges = new List<Edge>();
        public readonly int Number;

        public Node(int number)//конструктор
        {
            Number = number;
        }

        public override string ToString()
        {
            return Number.ToString();
        }
        public IEnumerable<Node> incidentNodes
        {
            get
            {
                foreach (var edge in IncidentEdges)
                {
                    yield return edge.OtherNode(this);
                }
            }
        }

        public IEnumerable<Edge> incidentEdges
        {
            get
            {
                foreach (var edge in incidentEdges)
                {
                    yield return edge;
                }
            }
        }

        public void Connect (Node anotherNode)
        {
            var edge = new Edge(this, anotherNode);
            IncidentEdges.Add(edge);
            anotherNode.IncidentEdges.Add(edge);
        }
    }
/*****************************************************/

class Program
    {
        static List<Node> BreadthSearch(Node startNode)//в ширину
        {
            var res = new List<Node>();
            var queue = new Queue<Node>();
            queue.Enqueue(startNode);
            var visited = new HashSet<Node>();
            while (queue.Count!=0)
            {
                var node = queue.Dequeue();
                if (visited.Contains(node)) continue;
                visited.Add(node);
                res.Add(node);

                foreach (var nextNode in node.incidentNodes)
                {
                    queue.Enqueue(nextNode);
                }
            }
            return res;
        }

        static List<Node> DepthSearch(Node startNode)//в глубину
        {
            var res = new List<Node>();
            var stack = new Stack<Node>();
            stack.Push(startNode);
            var visited = new HashSet<Node>();
            while (stack.Count != 0)
            {
                var node = stack.Pop();
                if (visited.Contains(node)) continue;
                visited.Add(node);
                res.Add(node);

                foreach (var nextNode in node.incidentNodes)
                {
                    stack.Push(nextNode);
                }
            }
            return res;
        }

        static void Main(string[] args)
        {
            var graph = Graph.MakeGraph(
                0, 1,
 
                0, 2,
 
                1, 3,
 
                1, 4,
 
                2, 3,
 
                2, 4);

            //graph.Connect(0, 4);
            foreach (var e in BreadthSearch(graph[0]))
            {
                Console.WriteLine(e.Number);
            }
        }
    }