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.*;
public class Codeforces
{
    static InputReader in=new InputReader(System.in);
    static OutputWriter out=new OutputWriter(System.out);    
    static StringBuilder sb=new StringBuilder();
    static long MOD = (long)(998244353);    
    // Main Class Starts Here        
        
    public static void main(String args[])throws IOException
    {
    	// Write your code.
    	int t = 1;
    	while(t-->0) {
    		int n=in();
    		int m=in();
    		String s[]=new String[n];
    		for(int i=0;i<n;i++) {
    			s[i] = sn();
    		}
    		StringBuilder fh=new StringBuilder();
    		StringBuilder sh=new StringBuilder();    		
    		for(int i=0;i<n;i++) {
    			for(int j=i+1;j<n;j++) {
    				boolean ch = isrev(s[i],s[j]);
    				if(ch) {
    					fh.append(s[i]);
    					sh.insert(0, s[j]);
    				}
    			}
    		}
    		for(int i=0;i<n;i++) {
    			if(pal(s[i])) {
    				fh.append(s[i]);
    				break;
    			}
    		}
    		if(fh.length() == 0) {
    			app(0+"\n");
    			continue;
    		}
    		fh.append(sh);
    		app(fh.length()+"\n"+fh+"\n");
    	}    	       	
    	out.printLine(sb);
    	out.close();
    }
    
    public static boolean pal(String s) {
    	StringBuilder str = new StringBuilder(s);
    	StringBuilder rev = new StringBuilder(s);
    	rev.reverse();
    	return rev.toString().equals(str.toString());
    }
    
    public static boolean isrev(String s,String t) {
    	StringBuilder str = new StringBuilder(s);
    	StringBuilder rev = new StringBuilder(t);
    	return ((rev.reverse()).toString()).equals(s.toString());
    }
    
    static class Pair{
    	int x;
    	int y;
    	public Pair(int x,int y) {
    	this.x=x;
    	this.y=y;
    	}
    }
               
    public static long rev(long n) {
    	if(n<10L)
    		return n;
    	long rev = 0L;
    	while(n != 0L) {
    		long a = n % 10L;
    		rev = a + rev*10L;
    		n /= 10L;
    	}
    	return rev;
    }
    
    public static long pow(long a,long b) {
    	if(b==0)
    		return 1L;
    	if(b==1)
    		return a % MOD;
    	long f = a * a;
    	if(f > MOD)
    		f %= MOD;
    	long val = pow(f, b/2) % MOD;
    	if(b % 2 == 0)
    		return val;
    	else {
    		long temp = val * (a % MOD);
    		if(temp > MOD)
    			temp = temp % MOD;
    		return temp;
    	}
    }
    
    public static int gcd(int a,int b) {
    	if(b==0)
    		return a;
    	return gcd(b, a%b);
    }
    
    public static int[] an(int n) {
    	int ar[]=new int[n];
    	for(int i=0;i<n;i++)
    		ar[i]=in();
    	return ar;
    }
    
    public static String atos(Object ar[]) {
    	return Arrays.toString(ar);
    }
    
    public static int in() {
    	return in.readInt();
    }
    
    public static long lin() {
    	return in.readLong();
    }    
    
    public static String sn() {
    	return in.readString();
    }
    
    public static void prln(Object o) {    	
    	out.printLine(o);
    }
    
    public static void prn(Object o) {    	
    	out.print(o);
    }
    
    public static int getMax(int a[]) {
    	int n = a.length;
    	int max = a[0];
    	for(int i=1; i < n; i++) {
    		max = Math.max(max, a[i]);
    	}
    	return max;
    }
    
    public static int getMin(int a[]) {
    	int n = a.length;
    	int min = a[0];
    	for(int i=1; i < n; i++) {
    		min = Math.min(min, a[i]);
    	}
    	return min;
    }
    
    public static void display(int a[]) {
    	out.printLine(Arrays.toString(a));
    }    
    
    public static HashMap<Integer,Integer> hm(int a[]){
    	HashMap<Integer,Integer> map=new HashMap<>();
    	for(int i=0; i < a.length;i++) {
    		int keep = (int)map.getOrDefault(a[i],0);
    		map.put(a[i],++keep);
    	}
    	return map;
    }
    
    public static void app(Object o) {
    	sb.append(o);
    }
    
    public static long calcManhattanDist(int x1,int y1,int x2,int y2) {
    	long xa = Math.abs(x1-x2);
    	long ya = Math.abs(y1-y2);
    	return (xa+ya);
    }
    
    static class Point
    {
    	int x;
    	int y;
    	String dir;
    	public Point(int x,int y,String dir) {
    		this.x=x;
    		this.y=y;
    		this.dir=dir;
    	}
    }    
    
    
    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;

        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 int readInt() {
            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 readLong() {
            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 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);
        }
    }

    static class OutputWriter {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream) {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer) {
            this.writer = new PrintWriter(writer);
        }

        public void print(Object...objects) {
            for (int i = 0; i < objects.length; i++) {
                if (i != 0)
                    writer.print(' ');
                writer.print(objects[i]);
            }
        }

        public void printLine(Object...objects) {
            print(objects);
            writer.println();
        }

        public void close() {
            writer.close();
        }
    } 
}