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.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;
import java.io.*;
public class Main
{
    public static void main(String args[]) throws IOException
    {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            int n = Integer.parseInt(reader.readLine());
            HashSet<String> hash = new HashSet<String>();
            HashSet<String> firstTime = new HashSet<String>();
            DisjointSet set = new DisjointSet();
            while(n-- !=0)
            {
                String str[] = reader.readLine().split(" ");
                if(!firstTime.contains(str[0]) && !hash.contains(str[1]) && !hash.contains(str[0]))
                    firstTime.add(str[0]);
                
                if(!hash.contains(str[0]))
                {
                    hash.add(str[0]);
                    set.makeSet(str[0]);
                }
                if(!hash.contains(str[1]))
                {
                    hash.add(str[1]);
                    set.makeSet(str[1]);
                }
                set.union(str[0], str[1]);
            }
            System.out.println(firstTime.size());
            for(String s : firstTime)
            {
                System.out.println(s+" "+set.findSet(s).data);
            }
        }
}
class Node
{
	String data ;
	int rank ;
	int count;
	Node parent ;
		
}
 
 
class DisjointSet 
{
	HashMap<String, Node> map ;
	
	public DisjointSet() {
		// TODO Auto-generated constructor stub
		map = new HashMap<String, Node>();
	}
		
	
	
	
	void makeSet(String data)
	{
		Node node = new Node();
		node.data = data;
		node.parent = node;
		node.count=1;
		node.rank = 0;
		map.put(data, node);
	}
	
	
	public Node findSet(String data) 
	{
	   // System.out.println(data);
        return findSet(map.get(data));
	}
	
	
	 private Node findSet(Node node) 
	 {
	        Node parent = node.parent;
	        if (parent == node) {
	            return parent;
	        }
	        node.parent = findSet(node.parent);
	        return node.parent;
	}
	 
	 public boolean union(String data1, String data2) 
	 {
	        Node node1 = map.get(data1);
	        Node node2 = map.get(data2);
 
	        Node parent1 = findSet(node1);
	        Node parent2 = findSet(node2);
 
	        //if they are part of same set do nothing
	        if (parent1.data == parent2.data) {
	            return false;
	        }
 
	 
	        if (parent1.rank < parent2.rank)
	        {
	            //increment rank only if both sets have same rank
	            parent1.rank = (parent1.rank == parent2.rank) ? parent1.rank + 1 : parent1.rank;
	            parent2.parent = parent1;

	        }
	        else
	        {
	            parent1.parent = parent2;
	        }
	        return true;
	}
	 
	 
	 public int findSize()
	 {
		 return map.size();
	 }
}