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.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        FastReader scan = new FastReader();
        //PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("taming.out")));
        PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
        Task solver = new Task();
        //int t = scan.nextInt();
        int t = 1;
        for(int i = 1; i <= t; i++) solver.solve(i, scan, out);
        out.close();
    }
    static class Task {
        public void solve(int testNumber, FastReader sc, PrintWriter pw) {
            HashSet<String> str = new HashSet<String>();
            int n = sc.nextInt();
            String[] arr = new String[n];
            int m = sc.nextInt();
            for(int i=0;i<n;i++){
                str.add(arr[i]=sc.nextLine());
            }
            StringBuilder total = new StringBuilder();
            for(String x : arr){
                str.remove(x);
                if(str.contains(reverse(x))){
                    total.append(x);
                    str.remove(reverse(x));
                }
            }
            String sm = "";
            loop:
            for(String x : arr){
                for(int i=0;i<m/2;i++){
                    //pw.println(x.charAt(i)+" "+x.charAt(m-i-1));
                    if(x.charAt(i)!=x.charAt(m-i-1)){
                        continue loop;
                    }
                }
                sm = x;
                break;
            }
            pw.println(total.length()*2+sm.length());
            pw.println(total.toString()+sm+total.reverse());
        }
        public String reverse (String a){
            StringBuilder x = new StringBuilder(a);
            return x.reverse().toString();
        }

    }
    static class tup implements Comparable<tup>{
        int a, b;
        tup(){};
        tup(int a, int b){
            this.a=a;
            this.b=b;
        }

        @Override
        public int compareTo( tup o2) {
            return o2.b!=b?Integer.compare(o2.b,b):Integer.compare(o2.a,a);
        }
    }

    static class bit {
        int n;
        int[] bit;
        public bit(int n) {
            this.n=n;
            bit=new int[n+1];
        }
        void add(int ind, int c) {
            for(; ind<n;ind|=(ind+1)) {
                bit[ind]=Math.max(bit[ind],c);
            }
        }
        int getMax(int r) {
            int ret = Integer.MIN_VALUE;
            for (; r >= 0; r = (r & (r + 1)) - 1)
                ret = Math.max(ret, bit[r]);
            return ret;
        }
    }
    static void shuffle(long[] a) {
        Random get = new Random();
        for (int i = 0; i < a.length; i++) {
            int r = get.nextInt(a.length);
            long temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }
    static void shuffle(int[] a) {
        Random get = new Random();
        for (int i = 0; i < a.length; i++) {
            int r = get.nextInt(a.length);
            int temp = a[i];
            a[i] = a[r];
            a[r] = temp;
        }
    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        public FastReader(String s) throws FileNotFoundException {
            br = new BufferedReader(new FileReader(new File(s)));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

}