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.
/*	/ ﾌﾌ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀ム
	/ )\⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀  Y
	(⠀⠀| ( ͡° ͜ʖ ͡°）⠀⌒(⠀ ノ
	(⠀ ﾉ⌒ Y ⌒ヽ-く __／
	| _⠀｡ノ| ノ｡ |/
	(⠀ー '_人`ー ﾉ
	⠀|\ ￣ _人'彡ﾉ
	⠀ )\⠀⠀ ｡⠀⠀ /
	⠀⠀(\⠀ #⠀ /
	⠀/⠀⠀⠀/ὣ====================D-
	/⠀⠀⠀/⠀ \ \⠀⠀\
	( (⠀)⠀⠀⠀⠀ ) ).⠀)
	(⠀⠀)⠀⠀⠀⠀⠀( | /
	|⠀ /⠀⠀⠀⠀⠀⠀ | /
	[_] ⠀⠀⠀⠀⠀[___]                     */
// Main Code at the Bottom
import java.util.*;
import java.lang.*;
import java.io.*;
import java.math.BigInteger; 
public class Main {
	//Fast IO class
    static class FastReader {
        BufferedReader br; 
        StringTokenizer st; 
        public FastReader() {
        	boolean env=System.getProperty("ONLINE_JUDGE") != null;
        	if(!env) {
        		try {
					br=new BufferedReader(new FileReader("src\\input.txt"));
				} catch (FileNotFoundException e) {
					e.printStackTrace();
				}
        	}
        	else 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 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; 
        } 
    }     
    static long MOD=1000000000+7;
    //Euclidean Algorithm
    static long gcd(long A,long B){
    	return (B==0)?A:gcd(B,A%B);
    }
    //Modular Exponentiation
    static long fastExpo(long x,long n){
        if(n==0) return 1;
        if((n&1)==0) return fastExpo((x*x)%MOD,n/2)%MOD;
        return ((x%MOD)*fastExpo((x*x)%MOD,(n-1)/2))%MOD;
    }
    //Modular Inverse
    static long inverse(long x) {
    	return fastExpo(x,MOD-2);
    }
    //Prime Number Algorithm
    static boolean isPrime(long n){
        if(n<=1) return false;
        if(n<=3) return true;
        if(n%2==0 || n%3==0) return false;
        for(int i=5;i*i<=n;i+=6) if(n%i==0 || n%(i+2)==0) return false;
        return true;
    }
    //Reverse an array
    static void reverse(int arr[],int l,int r){
    	while(l<r) {
    		int tmp=arr[l];
    		arr[l++]=arr[r];
    		arr[r++]=tmp;
    	}
    }
    //Print array
    static void print1d(int arr[]) {
    	out.println(Arrays.toString(arr));
    }
    static void print2d(int arr[][]) {
    	for(int a[]: arr) out.println(Arrays.toString(a));
    }
    // Pair
    static class pair{
    	int x,y;
    	pair(int a,int b){
    		this.x=a;
    		this.y=b;
    	}
    	public boolean equals(Object obj) {
    		if(obj == null || obj.getClass()!= this.getClass()) return false;
            pair p = (pair) obj;
            return (this.x==p.x && this.y==p.y);
        }
    	public int hashCode() {
            return Objects.hash(x,y);
        }
    }
    static FastReader sc=new FastReader();
    static PrintWriter out=new PrintWriter(System.out);  
    //Main function(The main code starts from here)
    static class obj{
    	StringBuilder x,y;
    	obj(StringBuilder a,StringBuilder b){
    		x=a;
    		y=b;
    	}
    }
    public static void main (String[] args) throws java.lang.Exception {
    	int test;
    	test=1;
    	//test=sc.nextInt();
        while(test-->0) {
        	int n=sc.nextInt(),m=sc.nextInt();
        	StringBuilder a[]=new StringBuilder[n];
        	for(int i=0;i<n;i++) {
        		a[i]=new StringBuilder(sc.nextLine());
        	}
        	ArrayList<obj> tmp=new ArrayList<>();
        	StringBuilder k=new StringBuilder();
        	int visited[]=new int[n];
        	for(int i=0;i<n;i++) {
        		int flag=0;
        		//out.println(a[i]);
        		for(int j=i+1;j<n;j++) {
        			String x=a[i].toString();
        			String y=new StringBuilder(a[j].toString()).reverse().toString();
        			if(x.equals(y) && visited[i]==0 && visited[j]==0) {
        				tmp.add(new obj(a[i],a[j]));
        				visited[i]=1;
        				visited[j]=1;
        				flag=1;
        				break;
        			}
        		}
        		if(flag==1) continue;
        		if(visited[i]==1) continue;
        		String x=a[i].toString(),y=a[i].reverse().toString();
        		if(x.equals(y)) {
        			if(a[i].length()>k.length() && visited[i]==0) {
        				k=a[i];
        			}
        		}
        	}
        	String ans="";
        	int l=tmp.size();
        	for(obj p: tmp) ans+=p.x;
        	ans+=k;
        	for(int i=l-1;i>=0;i--) {
        		ans+=tmp.get(i).y;
        	}
        	out.println(ans.length());
        	out.println(ans);
        } 	
        out.flush();
        out.close();
    }
}