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.*;
import java.util.*;

public class b285 {

	static class Task {		
		
		public void Solve(InputReader in,PrintWriter out)
		{
			int n=in.nextInt();
			HashMap<String, String> hm=new HashMap<String, String>();
			TreeMap<String, String> tm=new TreeMap<String, String>();
			HashSet<String> temp=new HashSet<String>();
			String s[][]=new String[n][2];
			for(int i=0;i<n;i++)
			{
				s[i][0]=in.next();
				s[i][1]=in.next();
				hm.put(s[i][0], s[i][1]);
			}
			boolean vis[]=new boolean[n];
			for(int i=0;i<n;i++)
			{
				if(vis[i])
					continue;
				String t1=s[i][0];
				String t2=t1;
			    while(hm.containsKey(t2))
			    {
			    	String t3=hm.get(t2);
			    	t2=t3;
			    	temp.add(t2);
			    }
			    if(!temp.contains(t1))
			        tm.put(t1, t2);
			}
			System.out.println(tm.size());
			for(Map.Entry<String, String> key:tm.entrySet())
				System.out.println(key.getKey()+" "+key.getValue());
		}
	}
	
    public static void main(String[] args) {
        InputReader in = new InputReader(System.in);
        PrintWriter out = new PrintWriter(System.out);
        Task solve = new Task();
        solve.Solve(in,out);
        out.close();
    }
    
    static void sort(int arr[][]){
        Arrays.sort(arr,new Comparator<int[]>(){
        public int compare(int[] a, int[] b) {
            return a[0]-b[0];
        }});
    }
    
    static void sort(int arr[]){
		int cnt[]=new int[(1<<16)+1];
		int ys[]=new int[arr.length];	
		for(int j=0;j<=16;j+=16){
			Arrays.fill(cnt,0);
			for(int x:arr){cnt[(x>>j&0xFFFF)+1]++;}
			for(int i=1;i<cnt.length;i++){cnt[i]+=cnt[i-1];}
			for(int x:arr){ys[cnt[x>>j&0xFFFF]++]=x;}
			{ final int t[]=arr;arr=ys;ys=t;}
		}
		if(arr[0]<0||arr[arr.length-1]>=0)return;
		int i,j,c;
		for(i=arr.length-1,c=0;arr[i]<0;i--,c++){ys[c]=arr[i];}
		for(j=arr.length-1;i>=0;i--,j--){arr[j]=arr[i];}
		for(i=c-1;i>=0;i--){arr[i]=ys[c-1-i];}
	}
    
	static int[] di={1,0,-1,0,1,-1,-1,1};
	static int[] dj={0,1,0,-1,1,1,-1,-1};

    static int min(int x,int y){return x<y?x:y;}
    static int max(int x,int y){return x>y?x:y;}
    static int lcm(int a,int b){return a*b/gcd(a,b);}
    static int gcd(int a,int b){return b==0?a:gcd(b,a%b);} 
    static int abs(int x){if(x>=0)return x;else return -x;}

    static long min(long x,long y){return x<y?x:y;}
    static long max(long x,long y){return x>y?x:y;}
    static long lcm(long a,long b){return a*b/gcd(a,b);}
    static long gcd(long a,long b){return b==0?a:gcd(b,a%b);}
    static long abs(long x){if(x>=0)return x;else return -x;}

    static void joutArray(int arr[]){
    	for(int i=0;i<arr.length;i++){
    		System.out.print(arr[i]+" ");
    	}
    	System.out.println();
    }
    
    static void joutArray(int arr[][],int n,int m){
    	for(int i=0;i<n;i++){
    		for(int j=0;j<m;j++)
    		System.out.print(arr[i][j]+" ");
    		System.out.println();
    	}
    	System.out.println();
    }

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

        public int nextInt() {
            return Integer.parseInt(next());
        }
        
        public long nextLong() {
        	return Long.parseLong(next());
        }
        
        public double nextDouble() {
        	return Double.parseDouble(next());
        }
        
        public int[] nextIntArray(int n) {
        	int arr[]=new int[n];
        	for(int i=0;i<n;i++)
        		arr[i]=nextInt();
        	return arr;
        }
        
        public char[] nextCharArray(){
        	char arr[]=next().toCharArray();
        	return arr;
        }
        
        public HashMap<Integer,Integer> nextHashMap(int n){
        	HashMap<Integer,Integer> hm=new HashMap<>();
        	for(int i=0;i<n;i++){
    			int num=nextInt();
    			hm.put(num,hm.get(num)==null?1:hm.get(num)+1);
    		}
        	return hm;
        }
     }
    
   }