using System;

using System.Collections.Generic;           

public class Program

{

    public static void Main()

    {

        char [][] ss = new  char [][] {new char[] {'a','b'}, new char[] {'a','e'}, new char[] {'a','c'} , new char[] {'b','e'} ,  new char[] {'b','d'},  new char[] {'c','b'} };

        Dictionary<char,List<char>> graph = new Dictionary<char,List<char>>{

        {'a', new List<char>()},

        {'b', new List<char>()},

            {'c', new List<char>()},

            {'d', new List<char>()},

            {'e', new List<char>()},

        };

        Dictionary<char,List<char>> dirctedGraph = new Dictionary<char,List<char>>();

        foreach(char [] edge in ss){

            if(!graph.ContainsKey(edge[0])){

                graph.Add(edge[0], new List<char>());

                graph[edge[0]].Add(edge[1]);

            }

            else{

                graph[edge[0]].Add(edge[1]);

            }

            if(!graph.ContainsKey(edge[1])){

                graph.Add(edge[1], new List<char>());

                graph[edge[1]].Add(edge[0]);

            }

            else{

                graph[edge[1]].Add(edge[0]);

            }

         }

        foreach(char [] edge in ss){

            if(!dirctedGraph.ContainsKey(edge[0])){

                dirctedGraph.Add(edge[0], new List<char>());

                dirctedGraph[edge[0]].Add(edge[1]);

            }

            else{

                dirctedGraph[edge[0]].Add(edge[1]);

            }

        }

        //dfss(graph,'a');

        dfss(dirctedGraph,'a');

    }

    public static void dfss(Dictionary<char,List<char>> graph,char source){

        Stack<char> s = new Stack<char>();

        s.Push(source);

        while(s.Count> 0){

            char current =s.Pop();

        Console.Out.WriteLine(current);

            foreach(char neighbor in graph[current]){

                s.Push(neighbor);

            }

        }

    }

}