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.*;
    import java.lang.Math; 
    import java.util.Arrays;
    import java.util.Scanner;
    import java.util.stream.IntStream;
    import java.io.OutputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.PrintWriter;
    import java.util.Arrays;
     
    public class Main {
       	public static void main(String[] args) {
    	   InputStream inputStream = System.in;
            OutputStream outputStream = System.out;
            Scanner in = new Scanner(inputStream);
            PrintWriter out = new PrintWriter(outputStream);
            TaskA solver = new TaskA();
            solver.solve(1, in, out);
            out.close();
    	}
    	
    	static class TaskA {
          public void solve(int testNumber, Scanner in, PrintWriter out) {
             int n = in.nextInt();
             Map<String, String> map = new TreeMap<String, String>();
             while(n-->0){
                  String a = in.next();
                  String b = in.next();
                 if(!map.containsKey(a)){ 
                       map.put(b,a);
                       
                 }else{
                     map.put(b, map.get(a));
                      map.remove(a);
                 }        
             }
             out.println(map.size());
             for(Map.Entry<String, String> entry : map.entrySet())
                   out.println(entry.getValue()+ " "+entry.getKey());
           
    	     }
    	     
    	    private String get( HashMap<String, String> map, String a){
    	         String S="";
    	         for (Map.Entry<String, String> entry : map.entrySet()){ 
                     if (entry.getValue().equals(a)){ 
                           S=entry.getKey();
                           break;
                     }
    	              
    	         }
               
              return S;          
    	    }  
     
    	}     
    	  	
    public int factorial(int n) {
            int fact = 1;
            int i = 1;
           while(i <= n) {
             fact *= i;
             i++;
           }
            return fact;
    }
     
    public static int BinarySearch(long temp,long[] sum,int r)
    {
    	int l=0;
    	
    	while(l<=r)
    	{
    		int mid=l+(r-l)/2;
    		if(sum[mid]==temp&&sum[mid]!=-1)
    		{
    		return mid;
    		}
    		if(sum[mid]>temp&&sum[mid]!=-1)
    			r=mid-1;
    		if(sum[mid]<temp&&sum[mid]!=-1)
    			l=mid+1;
        }
    	return -1;
    }
    public static long gcd(long x,long y)
    {
    	if(x%y==0)
    		return y;
    	else
    		return gcd(y,x%y);
    }
    public static int gcd(int x,int y)
    {
    	if(x%y==0)
    		return y;
    	else 
    		return gcd(y,x%y);
    }
    public static int abs(int a,int b)
    {
    	return (int)Math.abs(a-b);
    }
    public static long abs(long a,long b)
    {
    	return (long)Math.abs(a-b);
    }
    public static int max(int a,int b)
    {
    	if(a>b)
    		return a;
    	else
    		return b;
    }
    public static int min(int a,int b)
    {
    	if(a>b)
    		return b;
    	else 
    		return a;
    }
    public static long max(long a,long b)
    {
    	if(a>b)
    		return a;
    	else
    		return b;
    }
    public static long min(long a,long b)
    {
    	if(a>b)
    		return b;
    	else 
    		return a;
    }
     
     
    public static long pow(long n,long p,long m)
    {
    	 long  result = 1;
    	  if(p==0)
    	    return 1;
    	if (p==1)
    	    return n;
    	while(p!=0)
    	{
    	    if(p%2==1)
    	        result *= n;
    	    if(result>=m)
    	    result%=m;
    	    p >>=1;
    	    n*=n;
    	    if(n>=m)
    	    n%=m;
    	}
    	return result;
    }
    public static long pow(long n,long p)
    {
    	long  result = 1;
    	  if(p==0)
    	    return 1;
    	if (p==1)
    	    return n;
    	while(p!=0)
    	{
    	    if(p%2==1)
    	        result *= n;	    
    	    p >>=1;
    	    n*=n;	    
    	}
    	return result;
     
    }
     
    static long sort(int a[]){  
         int n=a.length;
    	int b[]=new int[n];	
    	return mergeSort(a,b,0,n-1);
         
    }
     
    static long mergeSort(int a[],int b[],long left,long right){
         long c=0;
         if(left<right){   
          long mid=left+(right-left)/2;
    	 c= mergeSort(a,b,left,mid);
    	 c+=mergeSort(a,b,mid+1,right);
    	 c+=merge(a,b,left,mid+1,right); 
         }	
    	return c;	 
    }
    static long merge(int a[],int  b[],long left,long mid,long right){
         long c=0;int i=(int)left;int j=(int)mid; int k=(int)left;
         while(i<=(int)mid-1&&j<=(int)right){ 
              if(a[i]<=a[j]){
                   b[k++]=a[i++]; 
              }
              else{ 
                   b[k++]=a[j++];c+=mid-i;
              }
         }
         
         while (i <= (int)mid - 1)   
                 b[k++] = a[i++]; 
         while (j <= (int)right)
                 b[k++] = a[j++];
         for (i=(int)left; i <= (int)right; i++) 
    	        a[i] = b[i];
    	        return c; 
         }
     
  }