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 javax.lang.model.util.ElementScanner6;
 
import java.io.*;
import java.text.DateFormat;
import java.text.SimpleDateFormat;

 
public class Main {
 
    public static void main(String[] args) {
         
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader inp = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Solver solver = new Solver();
        solver.solve(inp, out);
        out.close();
 
    }
 
 
 
 
 
    static class Solver {
 
        class pair implements Comparable<pair>{
 
            int i;
            int cnt;
            public pair(int i,int cnt)
            {
                this.i=i;
                this.cnt=cnt;
            }
 
            public int compareTo(pair p)
            {
                return Long.compare(this.i,p.i);
            }
 
        }
 
        class Node implements Comparable < Node > {
            int i;
            int cnt;
 
            Node(int i, int cnt) {
                this.i = i;
                this.cnt = cnt;
            }
 
            public int compareTo(Node n) {
                if (this.cnt == n.cnt) {
                    return Integer.compare(this.i, n.i);
                }
                return Integer.compare(this.cnt, n.cnt);
            }
        }
 
        public boolean done(int[] sp, int[] par) {
            int root;
 
            root = findSet(sp[0], par);
 
            for (int i = 1; i < sp.length; i++) {
                if (root != findSet(sp[i], par))
                    return false;
            }
            return true;
        }
        public int findSet(int i, int[] par) {
            int x = i;
            boolean flag = false;
            while (par[i] >= 0) {
                flag = true;
                i = par[i];
            }
            if (flag)
                par[x] = i;
            return i;
        }
 
        public void unionSet(int i, int j, int[] par) {
            int x = findSet(i, par);
            int y = findSet(j, par);
            if (x < y) {
                par[y] = x;
            } else {
                par[x] = y;
            }
        }
 
        public long pow(long a, long b, long MOD) {
            if (b == 0) {
                return 1;
            }
            if (b == 1) {
                return a;
            }
            long val = pow(a, b / 2, MOD);
            if (b % 2 == 0) {
                return val * val % MOD;
            } else {
                return val * (val * a % MOD) % MOD;
 
            }
 
        }
 
        public boolean isPrime(int n)
        {
            for(int i=2;i<n;i++)
            {
                if(n%i==0)
                {
                    return false;
                }
            }
            return true;
        }
 
 
        public void minPrimeFactor(int n, int[] s) {
            boolean prime[] = new boolean[n + 1];
            Arrays.fill(prime, true);
            s[1] = 1;
            s[2] = 2;
            for (int i = 4; i <= n; i += 2) {
                prime[i] = false;
                s[i] = 2;
            }
 
            for (int i = 3; i <= n; i += 2) {
                if (prime[i]) {
                    s[i] = i;
                    for (int j = 2 * i; j <= n; j += i) {
                        prime[j] = false;
                        s[j] = i;
                    }
                }
            }
 
        }
 
 
        public void findAllPrime(int n, ArrayList < Node > al, int s[]) {
            int curr = s[n];
            int cnt = 1;
            while (n > 1) {
                n /= s[n];
                if (curr == s[n]) {
                    cnt++;
                    continue;
 
                }
                Node n1 = new Node(curr, cnt);
                al.add(n1);
 
                curr = s[n];
                cnt = 1;
            }
        }
 
 
 
        public int binarySearch(int n, int k) {
            int left = 1;
            int right = 100000000 + 5;
            int ans = 0;
            while (left <= right) {
                int mid = (left + right) / 2;
                if (n / mid >= k) {
                    left = mid + 1;
                    ans = mid;
                } else {
                    right = mid - 1;
                }
            }
 
            return ans;
        }
        public boolean checkPallindrom(String s) {
            char ch[] = s.toCharArray();
 
            for (int i = 0; i < s.length() / 2; i++) {
                if (ch[i] != ch[s.length() - 1 - i])
                    return false;
            }
            return true;
        }

        public boolean pallindrom(String s1, String s2)
        {
            char ch[] = s1.toCharArray();
            char ch1[] = s2.toCharArray();

            for(int i=0;i<s1.length();i++)
            {
                if(ch[i]!=ch1[s1.length()-1-i])
                {
                    return false;
                }
            }

            return true;
        }
 
 
 
 
        public void remove(ArrayList < Integer > [] al, int x) {
            for (int i = 0; i < al.length; i++) {
                for (int j = 0; j < al[i].size(); j++) {
 
                    if (al[i].get(j) == x)
                        al[i].remove(j);
 
                }
            }
        }
 
        public long gcd(long a, long b) {
            if (a == 0)
                return b;
            return gcd(b % a, a);
        }
 
 
        public void printDivisors(long n, ArrayList < Long > al) {
            // Note that this loop runs till square root 
            for (long i = 1; i*i <= (n); i++) {
                if (n % i == 0) {
                    // If divisors are equal, print only one 
                    if (n / i == i) {
                        al.add(i);
                    } else // Otherwise print both 
                    {
                        al.add(i);
                        al.add(n / i);
                    }
 
                }
            }
        }
 
        public static long constructSegment(long seg[], long arr[], int low, int high, int pos) {
            if (low == high) {
                seg[pos] = arr[low];
                return seg[pos];
            }
            int mid = (low + high) / 2;
            long t1 = constructSegment(seg, arr, low, mid, (2 * pos) + 1);
            long t2 = constructSegment(seg, arr, mid + 1, high, (2 * pos) + 2);
            seg[pos] = t1 + t2;
            return seg[pos];
 
        }
        public static long querySegment(long seg[], int low, int high, int qlow, int qhigh, int pos) {
 
            if (qlow <= low && qhigh >= high) {
                return seg[pos];
            } else if (qlow > high || qhigh < low) {
                return 0;
            } else {
                long ans = 0;
                int mid = (low + high) / 2;
                ans += querySegment(seg, low, mid, qlow, qhigh, (2 * pos) + 1);
                ans += querySegment(seg, mid + 1, high, qlow, qhigh, (2 * pos) + 2);
                return ans;
            }
 
        }
        public static int lcs(char[] X, char[] Y, int m, int n) {
            if (m == 0 || n == 0)
                return 0;
            if (X[m - 1] == Y[n - 1])
                return 1 + lcs(X, Y, m - 1, n - 1);
            else
                return Integer.max(lcs(X, Y, m, n - 1), lcs(X, Y, m - 1, n));
        }
 
        public static long recursion(long start, long end, long cnt[], int a, int b) {
 
            long min = 0;
            long count = 0;
            int ans1 = -1;
            int ans2 = -1;
            int l = 0;
            int r = cnt.length - 1;
            while (l <= r) {
                int mid = (l + r) / 2;
                if (cnt[mid] >= start) {
                    ans1 = mid;
                    r = mid - 1;
                } else {
                    l = mid + 1;
                }
            }
 
            l = 0;
            r = cnt.length - 1;
            while (l <= r) {
                int mid = (l + r) / 2;
                if (cnt[mid] <= end) {
                    ans2 = mid;
                    l = mid + 1;
                } else {
                    r = mid - 1;
                }
            }
 
            if (ans1 == -1 || ans2 == -1 || ans2 < ans1) {
                // System.out.println("min1 "+min);
                min = a;
                return a;
 
            } else {
                min = b * (end - start + 1) * (ans2 - ans1 + 1);
            }
            if (start == end) {
                // System.out.println("min "+min);
                return min;
            }
            long mid = (end + start) / 2;
            min = Long.min(min, recursion(start, mid, cnt, a, b) + recursion(mid + 1, end, cnt, a, b));
            // System.out.println("min "+min);
            return min;
        }
 
 
        public int lowerBound(ArrayList<Long> al,long ele)
        {
            int l =0;
            int r =al.size()-1;
            int ans=-1;
            while(l<=r)
            {
                int mid = (l+r)/2;
                if(al.get(mid)<=ele)
                {
                    ans=mid;
                    l=mid+1;
                }
                else
                {
                    r=mid-1;
                }


            }
            return ans;
        }
        
        public int lowerBound(long arr[],long ele)
        {
            int l =0;
            int r =arr.length-1;
            int ans=-1;
            while(l<=r)
            {
                int mid = (l+r)/2;
                if(arr[mid]<=ele)
                {
                    ans=mid;
                    l=mid+1;
                }
                else
                {
                    r=mid-1;
                }


            }
            return ans;
        }
 
        public int dfs_util(ArrayList < Integer > [] al, boolean vis[], int x, int[] s, int lvl[]) {
 
            vis[x] = true;
            int cnt = 1;
            for (int i = 0; i < al[x].size(); i++) {
 
                if (!vis[al[x].get(i)]) {
                    lvl[al[x].get(i)] = lvl[x] + 1;
                    cnt += dfs_util(al, vis, al[x].get(i), s, lvl);
 
 
                }
 
 
            }
            s[x] = cnt;
            return s[x];
        }
 
        public void dfs(ArrayList[] al, int[] s, int[] lvl) {
 
            boolean vis[] = new boolean[al.length];
            for (int i = 0; i < al.length; i++) {
                if (!vis[i]) {
                    lvl[i] = 1;
                    dfs_util(al, vis, i, s, lvl);
                }
            }
        }
 

        public void permute(String s,int l, int r,ArrayList<String> al)
        {
            if(l==r)
            {
                al.add(s);
                
            }
            for(int i=l;i<=r;i++)
            {
                String str=swap(s,l,i);
                permute(str, l+1, r, al);
                
            }
        
        }

        public String swap(String s, int l, int r)
        {
            char ch[] = s.toCharArray();
            char tem = ch[l];
            ch[l]=ch[r];
            ch[r]=tem;
            return String.valueOf(ch);
        }
        

        public int[] computeLps(String s)
        {
            int ans[] =new int[s.length()];
            char ch[] = s.toCharArray();
            int n = s.length();
            int i=1;
            int len=0;
            ans[0]=0;
            while(i<n)
            {
                if(ch[i]==ch[len])
                {
                    len++;
                    ans[i]=len;
                    i++;
                }
                else
                {
                    if(len!=0)
                    {
                        len=ans[len-1];
                    }
                    else
                    {
                        ans[i]=len;
                        i++;
                    }
                }
            }
 
            return ans;
 
        }

        
 
       
 
        private void solve(InputReader inp, PrintWriter out1) {

            int n = inp.nextInt();
            int m = inp.nextInt();
            String s[] =new String[n];
            for(int i=0;i<n;i++)
            {
                s[i] = inp.next();
            }
            boolean d[] = new boolean[n];
            long ans=0;
            String f="";


            

            for(int i=0;i<n;i++)
            {
                if(d[i])
                {
                    continue;
                }
                for(int j=i+1;j<n;j++)
                {
                    if(d[j])
                        continue;
                    if(pallindrom(s[i], s[j]))
                    {
                        f+=s[j];
                        String temp =s[i];
                        temp+=f;
                        f=temp;
                        d[i] =true;
                        d[j] = true;
                        break;
                    }
                }
            }

            for(int i=0;i<n;i++)
            {
                if(checkPallindrom(s[i])&&!d[i])
                {
                    String temp = f;
                    f=f.substring(0, temp.length()/2);
                    f+=s[i];
                    f+=temp.substring((temp.length()/2),temp.length());
                    break;
                }
            }

            System.out.println(f.length());
            System.out.println(f);


        }
          
}
 
 
    static class InputReader {
        BufferedReader reader;
        StringTokenizer tokenizer;
 
        InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }
 
        String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }
 
        public int nextInt() {
            return Integer.parseInt(next());
        }
 
        public long nextLong() {
            return Long.parseLong(next());
        }
    }
}
class ele implements Comparable < ele > {
    int value;
    int i;
    boolean flag;
    public ele(int value, int i) {
        this.value = value;
        this.i = i;
        this.flag = false;
    }
    public int compareTo(ele e) {
        return Integer.compare(this.value, e.value);
    }
}