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.util.*;
import java.io.*;
import java.math.BigInteger;
public class Solution
{
     static class Pair<A,B>{
        A parent;
        B rank;
        Pair(A parent,B rank)
        {
            this.rank=rank;
            this.parent=parent;
        }
    }
//    static int find(Pair pr[],int i)
//    {
//        if(i==pr[i].parent)
//            return i;
//        else
//        {
//            pr[i].parent=find(pr,pr[i].parent);
//            return pr[i].parent;
//        }
//    }
//    static void join(Pair[] pr,int i,int j)
//    {
//        i=find(pr,i);
//        j=find(pr,j);
//        if(i==j)
//            return;
//        if(pr[i].rank>=pr[j].rank)
//        {
//            pr[j].parent=i;
//            pr[i].rank+=pr[j].rank;
//        }
//        else
//        {
//            pr[i].parent = j;
//            pr[j].rank+=pr[i].rank;
//        }
//    }
    static void swap(char ar[],int i,int j)
    {
        char f = ar[i];
        ar[i]=ar[j];
        ar[j]=f;
    }
    static ArrayList<Integer> graph[] ;
    static TreeSet<Long> ts;
    public static void main (String[] args) throws IOException
    {
        StringBuilder sb = new StringBuilder();
        FastReader s1 = new FastReader();
            int n=s1.I();
            int m=s1.I();
            StringBuilder palu = new StringBuilder();
            StringBuilder pald = new StringBuilder();
            HashSet<String> hs = new HashSet<>();
            HashSet<String> dup = new HashSet<>();
            HashSet<String> ext = new HashSet<>();
            for(int i=0;i<n;i++)
            {
                String g=s1.next();
                hs.add(g);
                dup.add(g);
            }
            while(!hs.isEmpty())
            {
//                hs.
                for(String temp:dup)
                {
                    StringBuilder rev = (new StringBuilder(temp).reverse());
                     if(isPall(temp))
                    {
                        ext.add(temp);
                        hs.remove(temp);
                    }
                     else if(hs.contains(rev.toString()))
                    {
                        hs.remove(rev);
                        hs.remove(temp);
                        palu.append(temp);
                        pald=rev.append(pald);
                    }
                    else
                    {
                        hs.remove(temp);
                    }
                }
                dup=new HashSet<>(hs);
            }
            if(!ext.isEmpty())
            {
                int i=0;
                for(String s:ext)
                {
                    palu.append(s);
                    i++;
                    if(i==1)
                        break;
                }
            }
            sb.append(palu).append(pald);
        System.out.println(sb.length()+"\n"+sb);
    }
    static boolean isPall(String s)
    {
        int n=s.length();
        int l=0;
        int r=n-1;
        while(l<r)
        {
            if(s.charAt(l)==s.charAt(r))
            {
                l++;
                r--;
            }
            else
                return false;
        }
        return true;
    }
    static int dayofweek(long d, int m, long y) 
{ 
    int t[] = { 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4 }; 
    y -= (m < 3) ? 1 : 0; 
    return (int)( y + y/4 - y/100 + y/400 + t[(m-1)] + d) % 7; 
}
        static String preprocess(String s)
    {
        StringBuilder sb = new StringBuilder();
        sb.append("@#");
        for(int i=0;i<s.length();i++)
        {
            sb.append(s.charAt(i)).append("#");
        }
        sb.append("$");
        return sb.toString();
    }
    static String LPS(String s)
    {
        String snew = preprocess(s);
        int n = snew.length();
//        System.out.println(snew);
        int c = 0,r = 0;
        int maxlen = 0;
        int index=0;
        int len[] = new int[n];
        for(int i=1;i<n-1;i++)
        {
            int mirr = c-(i-c);
            if(i<r)
            {
                len[i]=Math.min(len[mirr],r-i);
            }
      //      System.out.println(i+" ");
            while(snew.charAt(i+len[i])==snew.charAt(i-len[i]))
                len[i]++;
            if(i+len[i]>r)
            {
                c = i;
                r = i+len[i];
            }
//            System.out.println(c+" "+i+" "+snew.charAt(i)+" "+len[i]+" "+maxlen+" "+index);
            if(len[i]>maxlen)
            {
//                System.out.println("inside");
                maxlen = len[i];
                index = i;
            }
        }
        maxlen--;
        int left = (index-maxlen-1)/2;
        int right = left+maxlen;
        return s.substring(left, right);
    }
    static long phi(long n)
    {
        long result=n;
        for(int i=2;i<=Math.sqrt(n);i++)
        {
            if(n%i==0)
            {
                result-=result/i;
            }
            while(n%i==0)
            {
                n=n/i;
            }
        }
        if(n>1)
        {
            result-=(result/n);
        }
        return result;
    }
    static ArrayList<Integer> primeFactor(int n)
    {
        ArrayList<Integer> ans = new ArrayList<>();
        if(n%2==0)
            ans.add(2);
        while (n%2==0)
        {   
            n /= 2;
        }
        for (int i = 3; i <= Math.sqrt(n); i+= 2)
        {
            if(n%i==0)
                ans.add(i);
            while (n%i == 0)
            {
                n /= i;
            }
        }
        if (n > 2)
            ans.add(n);
        return ans;
    }
    static int longestSubSeg(int a[], int n,int k)
    {
        int cnt0 = 0;
        int l = 0;
        int max_len = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] == 0)
                cnt0++;
            while (cnt0 > k) {
                if (a[l] == 0)
                    cnt0--;
                l++;
            }
            max_len = Math.max(max_len, i - l + 1);
        }
        
        return max_len;
    }
    static void dfs(int index,boolean ar[])
    {
        ar[index]=true;
        for(int i=0;i<graph[index].size();i++)
        {
            if(!ar[graph[index].get(i)])
            {
                dfs(graph[index].get(i),ar);
            }
        }
    }
    static int binary(int left,int right,int ar[],int no)
    {
        int mid=(left+right)/2;
        if(Math.abs(right-left)<=1)
        {
            if(no>=ar[right])
            {
                return right+1;
            }
            else if(no<ar[left])
            {
                return left;
            }
            else
            {
                return left+1;
            }
        }
        if(ar[mid]>no)
        {
            right=mid-1;
            return binary(left, right, ar, no);
        }
        else{
            left=mid;
            return binary(left, right, ar, no);
        }
    }
    static class FastReader{
        BufferedReader br;
        StringTokenizer st;
        public FastReader()
        {
            br = new BufferedReader(new
                             InputStreamReader(System.in));
        }
        String next()
        {
            while (st == null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch (IOException  e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }
        
        int I()
        {
            return Integer.parseInt(next());
        }
        
        long L()
        {
            return Long.parseLong(next());
        }
        
        double D()
        {
            return Double.parseDouble(next());
        }
        
        String nextLine()
        {
            String str = "";
            try
            {
                str = br.readLine();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }
    static long gcd(long a,long b)
    {
        if(a%b==0)
            return b;
        return gcd(b,a%b);
    }
    static float power(float x, int y)
    {
        float temp;
        if( y == 0)
            return 1;
        temp = power(x, y/2);
        
        if (y%2 == 0)
            return temp*temp;
        else
        {
            if(y > 0)
                return x * temp * temp;
            else
                return (temp * temp) / x;
        }
    }
    static long pow(long x, long y)
    {
        int p = 1000000007;
        long res = 1;
        x = x % p;
        while (y > 0)
        {
            if((y & 1)==1)
                res = (res * x) % p;
            y = y >> 1;
            x = (x * x) % p;
        }
        return res;
    }
    static ArrayList<Integer> sieveOfEratosthenes(int n)
    {
        ArrayList<Integer> arr=new ArrayList<Integer>();
        boolean prime[] = new boolean[n+1];
        for(int i=2;i<n;i++)
            prime[i] = true;
        
        for(int p = 2; p*p <=n; p++)
        {
            if(prime[p] == true)
            {
                arr.add(p);
                for(int i = p*p; i <= n; i += p)
                    prime[i] = false;
            }
        }
        return arr;
    }
}
