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:
///package CodeForce;
import java.io.*;
import java.util.*;
/**
 *
 * @author prabhat
 */
public class P501B{
    

	   static final int MAX1 = 1000000+10;
	   static final int MAX2 = 1000001;
	   static final long MOD = 1000000007;
	   static int phiSum[] = new int[MAX1];
	   static int phi[] = new int[MAX1];
	   static long[] res=new long[MAX1];
	   static int arr[];
	   static long BIT[];
	   static int n;
	   static boolean[] b;
	   static int[][] pascal;
	    public static void main(String[] args) throws IOException{
	       
	        InputReader in = new InputReader(System.in);
	        PrintWriter pw = new PrintWriter(System.out,true);
	       int q=in.ii();
         Map<String,String> data = new HashMap<String, String>();
        for (int i = 0; i < q; ++i){
            String name = in.next();
            String change = in.next();
            if (!data.containsKey(name))
            {
                data.put(name,name);
            }
            data.put(change,data.get(name));
            data.remove(name);
        }
        pw.println(data.size());
        for (String i : data.keySet()){
            pw.println(data.get(i)+" "+i);
        }
    
	       pw.close();
	    }
	    public static long nCr(long total, long choose)
		{
			if(total < choose)
				return 0;
			if(choose == 0 || choose == total)
				return 1;
			return nCr(total-1,choose-1)+nCr(total-1,choose);
		}
	    static void compute() {
	    		for (int i = 0; i < MAX1; i++) {
	    			phi[i] = 0;
	    		}
	          phi[1]=1;
	    		for (int i = 2; i < MAX1; i++) {
	    			if (phi[i] == 0) {
	    				phi[i] = i - 1;
	     
	    				for (int j = 2 * i; j < MAX1; j += i) {
	    					 if(phi[j]==0) phi[j] = j ;
	    					phi[j] -= (phi[j]/i);
	    				}
	    			}
	    		}
	     
	    		for (int i = 1; i < MAX1; i++) {
	    			for (int j = i, k = 1; j < MAX1; j += i,k++) {
	    				phiSum[j] += i * phi[k];
	    			}
	    		}
	    		//System.out.println(Arrays.toString(phiSum));
                /*botharrays  res and phisum gives the same arrays so please don't worry*/
	    		
	    		for(int i=1;i<MAX1;i++)
	    		{
	    			for(int j=i+i;j<MAX1;j+=i)
	    			{
	    			   res[j]=res[j]+1L*i*phi[j/i];
	    			}
	    		}
	    		for(int i=1;i<=1000000;i++)
	    			res[i]=res[i]+res[i-1];
	    	//System.out.println(Arrays.toString(res));
	    						
	    		
	    		
	    }
	    public static void Seive()
		{
			
			 b=new boolean[10000001];
			Arrays.fill(b, true);
			b[0]=false;
			b[1]=false;
			
			for(int i=2;i<=(10000000);i++)
			{
				if(b[i])
				{
					
				 for(int j=i*2;j<=10000000;j+=i)
					{
						     b[j]=false;
						
					}
				}
				
			}
			
		}
	    static int pascal(int i1,int j1)
	    {
	  	  pascal=new int[101][101];
	  	  for(int i=0;i<=100;i++)
	  	  {
	  		  pascal[i][0]=1;
	  		  for(int j=1;j<=i;j++)
	  		  {
	  			  pascal[i][j]=(int) ((pascal[i-1][j]+pascal[i-1][j-1])%MOD);
	  		  }
	  	  }
	  	  return pascal[i1][j1];
	    }
	    private static class DSU{
			int[] parent;
			int[] rank;
			int cnt;
			public DSU(int n){
				parent=new int[n];
				rank=new int[n];
				for(int i=0;i<n;i++){
					parent[i]=i;
					rank[i]=1;
				}
				cnt=n;
			}
			int find(int i){
		        while(parent[i] !=i){
		        	parent[i]=parent[parent[i]];
		        	i=parent[i];
		        }
		        return i;
		    }
			int Union(int x, int y){
		        int xset = find(x);
		        int yset = find(y);
		        if(xset!=yset)
		        	cnt--;
		        if(rank[xset]<rank[yset]){
		        	parent[xset] = yset;
			        rank[yset]+=rank[xset];
			        rank[xset]=0;
			        return yset;
		        }else{
		        	parent[yset]=xset;
		        	rank[xset]+=rank[yset];
		        	rank[yset]=0;
		        	return xset;
		        }
		    }
		}
	  public static int[][] packU(int n, int[] from, int[] to, int max) {
		    
		    int[][] g = new int[n][];
		    int[] p = new int[n];
		    for (int i = 0; i < max; i++) p[from[i]]++;
		    for (int i = 0; i < max; i++) p[to[i]]++;
		    for (int i = 0; i < n; i++) g[i] = new int[p[i]];
		    for (int i = 0; i < max; i++) {
		        g[from[i]][--p[from[i]]] = to[i];
		        g[to[i]][--p[to[i]]] = from[i];
		    }
		    return g;
		}
		public static int[][] parents3(int[][] g, int root) {
		    int n = g.length;
		    int[] par = new int[n];
		    Arrays.fill(par, -1);
	 
		    int[] depth = new int[n];
		    depth[0] = 0;
	 
		    int[] q = new int[n];
		    q[0] = root;
		    for (int p = 0, r = 1; p < r; p++) {
		        int cur = q[p];
		        for (int nex : g[cur]) {
		            if (par[cur] != nex) {
		                q[r++] = nex;
		                par[nex] = cur;
		                depth[nex] = depth[cur] + 1;
		            }
		        }
		    }
		    return new int[][]{par, q, depth};
		}
		public static int lower_bound(int[] nums, int target) {
	        int low = 0, high = nums.length - 1;
	        while (low < high) {
	            int mid = low + (high - low) / 2;
	            if (nums[mid] < target)
	                low = mid + 1;
	            else
	                high = mid;
	        }
	        return nums[low] == target ? low : -1;
	    }
	 
	    public static int upper_bound(int[] nums, int target) {
	        int low = 0, high = nums.length - 1;
	        while (low < high) {
	            int mid = low + (high + 1 - low) / 2;
	            if (nums[mid] > target)
	                high = mid - 1;
	            else
	                low = mid;
	        }
	        return nums[low] == target ? low : -1;
	    }
	  public static boolean palin(String s)
		{
		   int i=0;
		   int j=s.length()-1;
		   while(i<j)
		   {
			   if(s.charAt(i)==s.charAt(j))
			   {
				   i++;
				   j--;
			   }
			   else return false;     
		   }
		   return true;
		}
		
	    static boolean CountPs(String s,int n)
	       {
	    	boolean b=false;
	    	     char[] S=s.toCharArray();
		       int[][] dp=new int[n][n];
		       boolean[][] p=new boolean[n][n];
		       for(int i=0;i<n;i++)p[i][i]=true;
		     
		       for(int i=0;i<n-1;i++)
		       {
		    	   if(S[i]==S[i+1])
		    	   {
		    		p[i][i+1]=true;
		    		dp[i][i+1]=1;
		    		b=true;
		    	   }
		       }
		    
		       for(int gap=2;gap<n;gap++)
		       {
		    	   for(int i=0;i<n-gap;i++)
		    	   {
		    		   int j=gap+i;
		    		   if(S[i]==S[j]&&p[i+1][j-1]){p[i][j]=true;}
		    		  
		    		  if(p[i][j])
		    			   dp[i][j]=dp[i][j-1]+dp[i+1][j]+1-dp[i+1][j-1];
		    		   
		    		   else  dp[i][j]=dp[i][j-1]+dp[i+1][j]-dp[i+1][j-1];
		    		  
		    		   if(dp[i][j]>=1){b=true;}
		    	   }
		       }
		      
		    return b; 
	   // return dp[0][n-1];
		       
	    }
	  
	  
	  
	 
	 
	public static int gcd(int a,int b)
	{
		int res=1;
		while(a>0)
		{
			res=a;
			a=b%a;
			b=res;
		}
		return res;
	}
	 
	 
	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 class Edge implements Comparator<Edge> {
		private int u;
		private int v;
		private int w;
		public Edge() {
		}
		public Edge(int u, int v, int w) {
			this.u=u;
			this.v=v;
			this.w=w;
		}
		public int getU() {
			return u;
		}
		public void setU(int u) {
			this.u = u;
		}
		public int getV() {
			return v;
		}
		public void setV(int v) {
			this.v = v;
		}
		public int getW() {
			return w;
		}
		public void setW(int w) {
			this.w = w;
		      }
		public int compareTo(Edge e)
		  {
			return this.getW() - e.getW();
		}
		@Override
		public String toString() {
			return "Edge [u=" + u + ", v=" + v + ", w=" + w + "]";
		}
		@Override
		public int compare(Edge arg0, Edge arg1) {
			// TODO Auto-generated method stub
			return 0;
		}
	}
	 
	 
	 
	static class Pair implements Comparable<Pair>
	{
		int a,b;
		Pair (int a,int b)
		{
			this.a=a;
			this.b=b;
		}
	 
		public int compareTo(Pair o) {
			// TODO Auto-generated method stub
			if(this.a!=o.a)
			return -Integer.compare(this.a,o.a);
			else
				return -Integer.compare(this.b, o.b);
			//return 0;
		}
		public boolean equals(Object o) {
	       if (o instanceof Pair) {
	           Pair p = (Pair)o;
	           return p.a == a && p.b == b;
	       }
	       return false;
	   }
	   public int hashCode() {
	       return new Integer(a).hashCode() * 31 + new Integer(b).hashCode();
	   }
	}
	 
		static class InputReader
		{
			private InputStream stream;
			private byte[] buf = new byte[1024];
			private int curChar;
			private int numChars;
			private SpaceCharFilter filter;
			
			public InputReader(InputStream stream)
			{
				this.stream = stream;
			}
			
			public int read()
			{
				if (numChars==-1) 
					throw new InputMismatchException();
				
				if (curChar >= numChars)
				{
					curChar = 0;
					try 
					{
						numChars = stream.read(buf);
					}
					catch (IOException e)
					{
						throw new InputMismatchException();
					}
					
					if(numChars <= 0)				
						return -1;
				}
				return buf[curChar++];
			}
		 
			public String nextLine()
			{
				BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
				String str = "";
	            try
	            {
	                str = br.readLine();
	            }
	            catch (IOException e)
	            {
	                e.printStackTrace();
	            }
	            return str;
			}
			public int ii()
			{
				int c = read();
				
				while(isSpaceChar(c)) 
					c = read();
				
				int sgn = 1;
				
				if (c == '-') 
				{
					sgn = -1;
					c = read();
				}
				
				int res = 0;
				do 
				{
					if(c<'0'||c>'9') 
						throw new InputMismatchException();
					res *= 10;
					res += c - '0';
					c = read();
				}
				while (!isSpaceChar(c)); 
				
				return res * sgn;
			}
			
			public long il() 
			{
				int c = read();
				while (isSpaceChar(c))
					c = read();
				int sgn = 1;
				if (c == '-') 
				{
					sgn = -1;
					c = read();
				}
				long res = 0;
				
				do 
				{
					if (c < '0' || c > '9')
						throw new InputMismatchException();
					res *= 10;
					res += c - '0';
					c = read();
				}
				while (!isSpaceChar(c));
					return res * sgn;
			}
			
			public double nextDouble() 
			{
				int c = read();
				while (isSpaceChar(c))
					c = read();
				int sgn = 1;
				if (c == '-') 
				{
					sgn = -1;
					c = read();
				}
				double res = 0;
				while (!isSpaceChar(c) && c != '.') 
				{
					if (c == 'e' || c == 'E')
						return res * Math.pow(10, ii());
					if (c < '0' || c > '9')
						throw new InputMismatchException();
					res *= 10;
					res += c - '0';
					c = read();
				}
				if (c == '.') 
				{
					c = read();
					double m = 1;
					while (!isSpaceChar(c)) 
					{
						if (c == 'e' || c == 'E')
							return res * Math.pow(10, ii());
						if (c < '0' || c > '9')
							throw new InputMismatchException();
						m /= 10;
						res += (c - '0') * m;
						c = read();
					}
				}
				return res * sgn;
			}
			
			public String readString() 
			{
				int c = read();
				while (isSpaceChar(c))
					c = read();
				StringBuilder res = new StringBuilder();
				do 
				{
					res.appendCodePoint(c);
					c = read();
				} 
				while (!isSpaceChar(c));
				
				return res.toString();
			}
		 
			public boolean isSpaceChar(int c) 
			{
				if (filter != null)
					return filter.isSpaceChar(c);
				return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
			}
		 
			public String next() 
			{
				return readString();
			}
			
			public interface SpaceCharFilter 
			{
				public boolean isSpaceChar(int ch);
			}
		}
	}