Returning back to problem solving, Gildong is now studying about palindromes. He learned that a palindrome is a string that is the same as its reverse. For example, strings "pop", "noon", "x", and "kkkkkk" are palindromes, while strings "moon", "tv", and "abab" are not. An empty string is also a palindrome.

Gildong loves this concept so much, so he wants to play with it. He has n distinct strings of equal length m. He wants to discard some of the strings (possibly none or all) and reorder the remaining strings so that the concatenation becomes a palindrome. He also wants the palindrome to be as long as possible. Please help him find one.

Input

The first line contains two integers n and m (1 ≤ n ≤ 100, 1 ≤ m ≤ 50) — the number of strings and the length of each string.

Next n lines contain a string of length m each, consisting of lowercase Latin letters only. All strings are distinct.

Output

In the first line, print the length of the longest palindrome string you made.

In the second line, print that palindrome. If there are multiple answers, print any one of them. If the palindrome is empty, print an empty line or don't print this line at all.

Examples

Input


3 3
tab
one
bat


Output


6
tabbat


Input


4 2
oo
ox
xo
xx


Output


6
oxxxxo


Input


3 5
hello
codef
orces


Output


0



Input


9 4
abab
baba
abcd
bcde
cdef
defg
wxyz
zyxw
ijji


Output


20
ababwxyzijjizyxwbaba

Note

In the first example, "battab" is also a valid answer.

In the second example, there can be 4 different valid answers including the sample output. We are not going to provide any hints for what the others are.

In the third example, the empty string is the only valid palindrome string.
import java.io.*;
import java.time.*;
import java.util.*;
import java.math.*;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
public class Main
{    
    static long mod=1000000007l;
    static int max=Integer.MAX_VALUE,min=Integer.MIN_VALUE;
    static long maxl=Long.MAX_VALUE,minl=Long.MIN_VALUE;
    static BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    static StringTokenizer st;
    static int max(int a,int b){return Math.max(a,b);}
    static int min(int a,int b){return Math.min(a,b);}
    static int abs(int a){return Math.abs(a);}
    static long max(long a,long b){return Math.max(a,b);}
    static long min(long a,long b){return Math.min(a,b);}
    static long abs(long a){return Math.abs(a);}
    static int sq(int a){return (int)Math.sqrt(a);}
    static long sq(long a){return (long)Math.sqrt(a);}
    static int ncr(int n,int c,long m)
    {
        long a=1l;
        for(int x=n-c+1;x<=n;x++)a=((a*x)%m);
        long b=1l;
        for(int x=2;x<=c;x++)b=((b*x)%m);
        long v=(div((int)b,m-2,m)%m);
        return (int)((a*v)%m);
    }
    static int fib(int n) 
    { 
        double p=(1+Math.sqrt(5))/2; 
        return (int)Math.round(Math.pow(p,n)/Math.sqrt(5)); 
    }
    static boolean[] sieve(int n)
    {
        boolean bo[]=new boolean[n+1];
        bo[0]=true;bo[1]=true;
        for(int x=4;x<=n;x+=2)bo[x]=true;
        for(int x=3;x*x<=n;x+=2)
        {
            if(!bo[x])
            {
                for(int y=x*x;y<=n;y+=x)bo[y]=true;
            }
        }
        return bo;
    }
    static int[] fac(int n)
    {
        int bo[]=new int[n+1];
        bo[0]=0;bo[1]=1;
        for(int x=1;x<=n;x++)
        {
            for(int y=x;y<=n;y+=x)bo[y]++;
        }
        return bo;
    }
    static int gcd(int a,int b)
    {
        if(b==0)return a;
        return gcd(b,a%b);
    }
    static long div(long a,long b,long m) 
    {
        long r=1l;
        a%=m;  
        while(b>0)
        {
            if((b&1)==1)r=(r*a)%m; 
            b>>=1;
            a=(a*a)%m;  
        } 
        return r; 
    }
    static int i()throws IOException
    {
        if(!st.hasMoreTokens()) st=new StringTokenizer(br.readLine());
        return Integer.parseInt(st.nextToken());
    }
    static long l()throws IOException
    {
        if(!st.hasMoreTokens())st=new StringTokenizer(br.readLine());
        return Long.parseLong(st.nextToken());
    }
    static String s()throws IOException
    {
        if(!st.hasMoreTokens())st=new StringTokenizer(br.readLine());
        return st.nextToken();
    }
    static double d()throws IOException
    {
        if(!st.hasMoreTokens())st=new StringTokenizer(br.readLine());
        return Double.parseDouble(st.nextToken());
    }
    static char c()throws IOException
    {
        if(!st.hasMoreTokens())st=new StringTokenizer(br.readLine());
        return st.nextToken().charAt(0);
    }
    static boolean b()throws IOException
    {
        if(!st.hasMoreTokens())st=new StringTokenizer(br.readLine());
        return Boolean.parseBoolean(st.nextToken());
    }
    static void p(Object p){System.out.print(p);}
    static void p(String p){System.out.print(p);}
    static void p(int p){System.out.print(p);}
    static void p(double p){System.out.print(p);}
    static void p(long p){System.out.print(p);}
    static void p(char p){System.out.print(p);}
    static void p(boolean p){System.out.print(p);}
    static void pl(Object p){System.out.println(p);}
    static void pl(String p){System.out.println(p);}
    static void pl(int p){System.out.println(p);}
    static void pl(char p){System.out.println(p);}
    static void pl(double p){System.out.println(p);}
    static void pl(long p){System.out.println(p);}
    static void pl(boolean p){System.out.println(p);}
    static void pl(){System.out.println();}
    static int[] ari(int n)throws IOException
    {
        int ar[]=new int[n];
        st=new StringTokenizer(br.readLine());
        for(int x=0;x<n;x++) ar[x]=Integer.parseInt(st.nextToken());
        return ar;
    }
    static int[][] ari(int n,int m)throws IOException
    {
        int ar[][]=new int[n][m];
        for(int x=0;x<n;x++)
        {
            st=new StringTokenizer(br.readLine());
            for(int y=0;y<m;y++)ar[x][y]=Integer.parseInt(st.nextToken());
        }
        return ar;
    }
    static long[] arl(int n)throws IOException
    {
        long ar[]=new long[n];
        st=new StringTokenizer(br.readLine());
        for(int x=0;x<n;x++) ar[x]=Long.parseLong(st.nextToken());
        return ar;
    }
    static long[][] arl(int n,int m)throws IOException
    {
        long ar[][]=new long[n][m];
        for(int x=0;x<n;x++)
        {
            st=new StringTokenizer(br.readLine());
            for(int y=0;y<m;y++)ar[x][y]=Long.parseLong(st.nextToken());
        }
        return ar;
    }
    static String[] ars(int n)throws IOException
    {
        String ar[]=new String[n];
        st=new StringTokenizer(br.readLine());
        for(int x=0;x<n;x++) ar[x]=st.nextToken();
        return ar;
    }
    static double[] ard(int n)throws IOException
    {
        double ar[]=new double[n];
        st=new StringTokenizer(br.readLine());
        for(int x=0;x<n;x++)ar[x]=Double.parseDouble(st.nextToken());
        return ar;
    }
    static double[][] ard(int n,int m)throws IOException
    {
        double ar[][]=new double[n][m];
        for(int x=0;x<n;x++)
        {
            st=new StringTokenizer(br.readLine());
            for(int y=0;y<m;y++)ar[x][y]=Double.parseDouble(st.nextToken());
        }
        return ar;
    }
    static char[] arc(int n)throws IOException
    {
        char ar[]=new char[n];
        st=new StringTokenizer(br.readLine());
        for(int x=0;x<n;x++)ar[x]=st.nextToken().charAt(0);
        return ar;
    }
    static char[][] arc(int n,int m)throws IOException
    {
        char ar[][]=new char[n][m];
        for(int x=0;x<n;x++)
        {
            String s=br.readLine();
            for(int y=0;y<m;y++)ar[x][y]=s.charAt(y);
        }
        return ar;
    }
    static void p(int ar[])
    {
        StringBuilder sb=new StringBuilder("");;
        for(int a:ar) sb.append(a+" ");
        System.out.println(sb);
    }
    static void p(int ar[][])
    {
        StringBuilder sb;
        for(int a[]:ar)
        {
            sb=new StringBuilder("");
            for(int aa:a) sb.append(aa+" ");
            System.out.println(sb);
        }
    }
    static void p(long ar[])
    {
        StringBuilder sb=new StringBuilder("");
        for(long a:ar)sb.append(a+" ");
        System.out.println(sb);
    }
    static void p(long ar[][])
    {
        StringBuilder sb;
        for(long a[]:ar)
        {
            sb=new StringBuilder("");
            for(long aa:a)sb.append(aa+" ");
            System.out.println(sb);
        }
    }
    static void p(String ar[])
    {
        StringBuilder sb=new StringBuilder("");
        for(String a:ar)sb.append(a+" ");
        System.out.println(sb);
    }
    static void p(double ar[])
    {
        StringBuilder sb=new StringBuilder("");
        for(double a:ar)sb.append(a+" ");
        System.out.println(sb);
    }
    static void p(double ar[][])
    {
        StringBuilder sb;
        for(double a[]:ar)
        {
            sb=new StringBuilder("");
            for(double aa:a)sb.append(aa+" ");
            System.out.println(sb);
        }
    }
    static void p(char ar[])
    {
        StringBuilder sb=new StringBuilder("");
        for(char aa:ar)sb.append(aa+" ");
        System.out.println(sb);
    }
    static void p(char ar[][])
    {
        StringBuilder sb;
        for(char a[]:ar)
        {
            sb=new StringBuilder("");
            for(char aa:a)sb.append(aa+" ");
            System.out.println(sb);
        }
    }
    static public void main(String[] args)throws Exception
    {
        st=new StringTokenizer(br.readLine());
        int n=i();
        int m=i();
        int k=m/2;
        HashMap<String,Integer> h=new HashMap<>();
        HashSet<String> a=new HashSet<>();
        HashMap<String,Integer> hh=new HashMap<>();
        int co=0;
        while(n-->0)
        {
        	String s=s();
        	int f=0;
        	char ch[]=s.toCharArray();
        	for(int x=0;x<k;x++)
        	{
        		ch[x]^=ch[m-x-1];
        		ch[m-x-1]^=ch[x];
        		ch[x]^=ch[m-x-1];
        	}
        	String p=new String(ch);
        	if(p.equals(s))
        	{
        		Integer rr=h.get(p);
        		if(rr==null)h.put(p,1);
        		else h.put(p,rr+1);
        	}
        	else
        	{
	        	Integer q=hh.get(p);
	        	if(q==null)hh.put(p,1);
	        	else hh.put(p,q+1);
	        	a.add(s);
        	}
        	
        }
      
       StringBuilder ma=new StringBuilder("");
        for(String b:a)
        {
        	if(!hh.containsKey(b))continue;
        	int aa=hh.get(b);
        	char ch[]=b.toCharArray();
        	for(int x=0;x<k;x++)
        	{
        		ch[x]^=ch[m-x-1];
        		ch[m-x-1]^=ch[x];
        		ch[x]^=ch[m-x-1];
        	}
        	String p=new String(ch);
        	if(hh.containsKey(p))
        	{
        		int bb=hh.get(p);
        		int ii=min(bb,aa);
        		for(int y=0;y<ii;y++)ma.append(b);
        	}
        	hh.remove(b);
    		hh.remove(p);
        }
        int uu=0;
        String gg="";
        for(String ss:h.keySet())
        {
        	if(h.get(ss)%2==0)
    		{
        		int vv=h.get(ss);
        		for(int x=0;x<vv;x++)ma.append(ss);
    		}
        	else
    		{
        		int vv=h.get(ss)-1;
        		uu=1;
        		gg=new String(ss);
        		for(int x=0;x<vv;x++)ma.append(ss);
    		}
        }
        if(uu==0)
        {
        	String j=new StringBuilder(new String(ma)).reverse().toString();
        	ma.append(j);
        }
        else
        {
        	String j=new StringBuilder(new String(ma)).reverse().toString();
        	ma.append(gg+""+j);
        }
        pl(ma.length());
        pl(ma);
        
        
        
       
        
        
        
        
        
        
        
        
        
        
        
        
  
        
    }   
}