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 javax.swing.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.util.*;
 
 
public class simple1 implements Runnable {
 
	 
    public void run() {
 
        InputReader input = new InputReader(System.in);
        PrintWriter w = new PrintWriter(System.out);
        
        int  n=input.nextInt();
        int m =input.nextInt();
        
        
        HashSet<String> set  = new HashSet<>();
        String ans="";
        String eq="";
        int count=0;
        for(int i=0;i<n;i++)
        {
        	String s= input.next();
        	String s1=new StringBuilder(s).reverse().toString();
        	
        	if(s.equals(s1))
        	{
        		eq=s1;
        	}
        	if(set.contains(s1))
        	{
        		ans+=s;
        		ans=s1+ans;
        		set.remove(s1);
        		count++;
        	}
        	else
        		set.add(s);
        }
        if(eq.length()==m)
        {
        	ans=  ans.substring(0,count*m)+eq+ans.substring(count*m);
        }
        System.out.println(ans.length());
        System.out.println(ans);
        
    }
    
   
 
    static int ans(int[] arr, int n)
    {
    	
    	int max = arr[0] | arr[1];
    	
    	for(int i=1;i<n-1;i++)
    	{
    		max =Math.max(max, arr[i] | arr[i+1]);
    	}
    	return max;
    }
class Sorting implements Comparator<pair>
{
	public int compare(pair one, pair two)
	{
		if(one.a>two.a)
			return 1;
		else if(one.a==two.a)
			return 0;
		else 
			return -1;
				
	}
}
class pair
{
	int a;
	int b;
	
	pair(int a ,int b)
	{
		this.a=a;
		this.b=b;
	}
		
}
 
    class Graph{
        private final int v;
        private List<List<Integer>> adj;
        Graph(int v){
            this.v = v;
            adj = new ArrayList<>(v);
            for(int i=0;i<v;i++){
                adj.add(new LinkedList<>());
            }
        }
        private void addEdge(int a,int b){
            adj.get(a).add(b);
        }
        private boolean isCyclic()
        {
            boolean[] visited = new boolean[v];
            boolean[] recStack = new boolean[v];
            for (int i = 0; i < v; i++)
                if (isCyclicUtil(i, visited, recStack))
                    return true;
 
            return false;
        }
        private boolean isCyclicUtil(int i, boolean[] visited, boolean[] recStack)
        {
            if (recStack[i])
                return true;
            if (visited[i])
                return false;
            visited[i] = true;
            recStack[i] = true;
            List<Integer> children = adj.get(i);
            for (Integer c: children)
                if (isCyclicUtil(c, visited, recStack))
                    return true;
            recStack[i] = false;
            return false;
        }
    }
    public static void sortbyColumn(int arr[][], int col)
    {
 
        Arrays.sort(arr, new Comparator<int[]>()
        {
            public int compare(int[] o1, int[] o2){
                return(Integer.valueOf(o1[col]).compareTo(o2[col]));
            }
        });
 
    }
    static long gcd(long a, long b)
    {
        if (b == 0)
            return a;
        return gcd(b, a % b);
    }
    public static class DJSet {
        public int[] upper;
 
        public DJSet(int n) {
            upper = new int[n];
            Arrays.fill(upper, -1);
        }
 
        public int root(int x) {
            return upper[x] < 0 ? x : (upper[x] = root(upper[x]));
        }
 
        public boolean equiv(int x, int y) {
            return root(x) == root(y);
        }
 
        public boolean union(int x, int y) {
            x = root(x);
            y = root(y);
            if (x != y) {
                if (upper[y] < upper[x]) {
                    int d = x;
                    x = y;
                    y = d;
                }
                upper[x] += upper[y];
                upper[y] = x;
            }
            return x == y;
        }
    }
    public static int[] radixSort(int[] f)
    {
        int[] to = new int[f.length];
        {
            int[] b = new int[65537];
            for(int i = 0;i < f.length;i++)b[1+(f[i]&0xffff)]++;
            for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
            for(int i = 0;i < f.length;i++)to[b[f[i]&0xffff]++] = f[i];
            int[] d = f; f = to;to = d;
        }
        {
            int[] b = new int[65537];
            for(int i = 0;i < f.length;i++)b[1+(f[i]>>>16)]++;
            for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
            for(int i = 0;i < f.length;i++)to[b[f[i]>>>16]++] = f[i];
            int[] d = f; f = to;to = d;
        }
        return f;
    }
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;
        private BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
 
        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() {
            String str = "";
            try {
                str = br.readLine();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
        public int nextInt() {
            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 nextLong() {
            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, nextInt());
                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, nextInt());
                    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);
        }
    }
    public static void main(String args[]) throws Exception {
        new Thread(null, new simple1(),"TaskA",1<<26).start();
    }
}


