using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        string handleCountString = Console.ReadLine();

        int handleCount = Int32.Parse(handleCountString);

        var olds = new string[handleCount];

        var news = new string[handleCount];

        var map = new Dictionary<string, string>();

        var rmap = new Dictionary<string, string>();

        var used = new HashSet<string>();

        var res = new Dictionary<string, string>();

        for (int i = 0; i < handleCount; i++)

        {

            string handleInputString = Console.ReadLine();

            string[] handleInputStringSplit = handleInputString.Split(' ');

            olds[i] = handleInputStringSplit[0];

            news[i] = handleInputStringSplit[1];

            map[olds[i]] = news[i];

            rmap[news[i]] = olds[i];

        }

​

        for (int i = 0; i < handleCount; i++)

        {

            if (used.Contains(olds[i]) || used.Contains(news[i]))

            {

                continue;

            }

            while (rmap.ContainsKey(olds[i]))

            {

                used.Add(olds[i]);

                olds[i] = rmap[olds[i]];

            }

​

            while (map.ContainsKey(news[i]))

            {

                used.Add(news[i]);

                news[i] = map[news[i]];

            }

​

            res[olds[i]] = news[i];

            used.Add(olds[i]);

            used.Add(news[i]);

        }

        Console.WriteLine(res.Count);

​

        foreach (KeyValuePair<string, string> result in res)

        {

            Console.WriteLine(result.Key + " " + result.Value);

        }

    }

}