Problem: Misha hacked the Codeforces site. Then he decided to let all the users change their handles. A user can now change his handle any number of times. But each new handle must not be equal to any handle that is already used or that was used at some point.

Misha has a list of handle change requests. After completing the requests he wants to understand the relation between the original and the new handles of the users. Help him to do that.

Input

The first line contains integer q (1 ≤ q ≤ 1000), the number of handle change requests.

Next q lines contain the descriptions of the requests, one per line.

Each query consists of two non-empty strings old and new, separated by a space. The strings consist of lowercase and uppercase Latin letters and digits. Strings old and new are distinct. The lengths of the strings do not exceed 20.

The requests are given chronologically. In other words, by the moment of a query there is a single person with handle old, and handle new is not used and has not been used by anyone.

Output

In the first line output the integer n — the number of users that changed their handles at least once.

In the next n lines print the mapping between the old and the new handles of the users. Each of them must contain two strings, old and new, separated by a space, meaning that before the user had handle old, and after all the requests are completed, his handle is new. You may output lines in any order.

Each user who changes the handle must occur exactly once in this description.

Examples

Input

5
Misha ILoveCodeforces
Vasya Petrov
Petrov VasyaPetrov123
ILoveCodeforces MikeMirzayanov
Petya Ivanov


Output

3
Petya Ivanov
Misha MikeMirzayanov
Vasya VasyaPetrov123

Solution (in JAVA):

Solution:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Iterator;
import java.util.StringTokenizer;

public class Solution {

	//	public static final double eps = 1e-9;
	//	public static final int mod = 1000000007;
	//	public static final double pi = 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679;
	//	public static final int sievesize = (int) (1e6 + 10);
	//	public static boolean[] prime;
	//	public static final int dx[] = {1, -1, 0, 0};
	//	public static final int dy[] = {0, 0, 1, -1};

	public static void main(String[] args) throws IOException {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		OutputWriter out = new OutputWriter(outputStream);
		Task solver = new Task();
		solver.solve(1, in, out);
		out.close();
	}

	static class Task {

		public void solve(int testNumber, InputReader in, OutputWriter out) throws IOException {
			int q = in.nextInt();
			HashMap<String, String> map = new HashMap<>();
			int count = 0;
			while(q-- > 0) {
				String oldS = in.next(), newS = in.next();
				if(map.containsValue(oldS)) {
					Iterator<String> it = map.keySet().iterator();
					while(it.hasNext()) {
						String s = it.next();
						if(map.get(s).equals(oldS)) {
							map.put(s, newS);
							break;
						}
					}
				}
				else if(!map.containsKey(oldS)) {
					map.put(oldS, newS);
					count++;
				}
			}
			out.println(count);
			Iterator<String> it = map.keySet().iterator();
			while(it.hasNext()) {
				String s = it.next();
				out.println(s + " " + map.get(s));
			}
		}

	//        static class Node {
	//        	LinkedList<Integer> list;
	//        	
	//        	public Node() {
	//				list = new LinkedList<>();
	//			}
	//        }
	//        
	//        static class Pair implements Comparable<Pair> {
	//        	
	//        	long first, second;
	//        	
	//        	public Pair(long first, long second) {
	//        		this.first = first;
	//				this.second = second;
	//			}
	//
	//			@Override
	//			public int compareTo(Pair o) {
	//				return (int) (this.second-o.second);
	//			}	
	//        }
}

//	public static int[] shuffle(int arr[], Random gen) {
//		for(int i = 0, n = arr.length; i < n; i++)
//		{
//			int index = gen.nextInt(n - i) + i;
//			int temp = arr[i];
//			arr[i] = arr[index];
//			arr[index] = temp;
//		}
//		return arr;
//	}
//
//	public static boolean triangle(long a, long b, long c){
//	    return ((a+b) > c && (b+c) >a && (a+c) > b);
//	}
//		
//	public static boolean isPerfectSquare(long n){
//		if (n < 0) 
//	    	return false;
//	    long test = (long) (Math.sqrt(n) + 0.5);
//	    return test*test == n;
//	}
//		
//	public static int isnum(char s){
//		if(s=='1' || s=='2' || s=='3' || s=='4' || s=='5' || s=='6' || s=='7' || s=='8' || s=='9' || s=='0') 
//	    	return 1; 
//		return 0;
//	}
//		
//	public static long nextPowerOf2(long n){
//	    n--;
//	    n |= n >> 1;
//	    n |= n >> 2;
//	    n |= n >> 4;
//	    n |= n >> 8;
//	    n |= n >> 16;
//	    n++;
//	    return n;
//	}
//		
//	public static int gcd(int a, int b){
//	    int t; 
//	    while (b > 0){ 
//	    	a = a%b; 
//	    	t = a; 
//	    	a = b; 
//	    	b = t; 
//    	}
//	    return a;
//	}
//		
//	public static void sieve(int n){
//		prime=new boolean[sievesize+1];
//		Arrays.fill(prime, true);
//	    long x, y; 
//	    for(x = 2; x * x <= sievesize; x++)
//	    { 
//	    	if(prime[(int) x])
//	    		for(y = x * 2; y <= sievesize; y += x) 
//	    			prime[(int) y]=false; 
//	    }
//	}

static class InputReader {
	public BufferedReader reader;
	public StringTokenizer tokenizer;

	public InputReader(InputStream stream) {
		reader = new BufferedReader(new InputStreamReader(stream), 32768);
		tokenizer = null;
	}

	public String next() {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(reader.readLine());
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken();
	}

	public int nextInt() {
		return Integer.parseInt(next());
	}

	public long nextLong() {
		return Long.parseLong(next());
	}

	public int[] nextIntArray(int size) {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(reader.readLine());
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
		int[] arr=new int[size];
		for(int i = 0; i < size; i++) 
			arr[i] = Integer.parseInt(tokenizer.nextToken());
		return arr;
	}

	public long[] nextLongArray(int size) {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(reader.readLine());
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
		long[] arr=new long[size];
		for(int i = 0; i < size; i++) 
			arr[i] = Long.parseLong(tokenizer.nextToken());
		return arr;
	}

	public double[] nextDoubleArray(int size) {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(reader.readLine());
			} catch (IOException e) {
				throw new RuntimeException(e);
			}
		}
		double[] arr=new double[size];
		for(int i = 0; i < size; i++) 
			arr[i] = Double.parseDouble(tokenizer.nextToken());
		return arr;
	}

	public String[] nextStringArray(int size) throws IOException {
		String[] arr=new String[size];
		for(int i = 0; i < size; i++) 
			arr[i] = reader.readLine();
		return arr;
	}

	public char[] nextCharArray(int size) throws IOException {
		char[] arr=reader.readLine().toCharArray();
		return arr;
	}
}

static class OutputWriter {
	public PrintWriter pw;

	public OutputWriter(OutputStream stream) {
		pw = new PrintWriter(stream);
	}

	public void println(Object str) {
		pw.println(str);
	}

	public void print(Object str) {
		pw.print(str + " ");
	}

	public void close() {
		pw.close();
	}

	public void flush() {
		pw.flush();
	}

	public void printStringArray(String[] arr) {
		for(int i = 0; i < arr.length; i++)
			pw.println(arr[i]);
	}

	public void printIntArray(int[] arr) {
		for(int i = 0; i < arr.length; i++)
			pw.print(arr[i] + " ");
	}

	public void printLongArray(long[] arr) {
		for(int i = 0; i < arr.length; i++)
			pw.print(arr[i] + " ");
	}

	public void printCharArray(char[] arr) {
		for(int i = 0; i < arr.length; i++)
			pw.print(arr[i] + " ");
	}

	public void printFloatArray(float[] arr) {
		for(int i = 0; i < arr.length; i++)
			pw.print(arr[i] + " ");
	}

	public void printDoubleArray(double[] arr) {
		for(int i = 0; i < arr.length; i++)
			pw.print(arr[i] + " ");
	}
}
}