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.math.BigInteger; 
import java.util.*;
import java.math.*; 

//Mann Shah [ DAIICT ].
//fast io

public class Main {
	static long mod = (long) (1e9+7);
	static long mm = (long)(1e9+6);
	static long N = (long)(2*1e5);
	static InputReader in;
    static PrintWriter out;
    static Debugger deb;
    
    
    public static int lower_bound(long[] a,int k) { // no. of elements less than k in array.
    		int first = 0,last = a.length,mid;
        while (first < last) {
            mid = first + ((last - first) >> 1); 
            if (a[mid] < k)  //lower bound. for upper use <= ( n - first)
                first = mid + 1; 
            else 
                last = mid;
        }
    		return first;
    }
    
    public static int gcd(int a, int b){ 
	    if (a == 0) 
	        return b;  
	    return gcd(b % a, a);  
    } 
    
    public static long power(long x, long y, long p) 
    { 
        long res = 1;      
        x = x % p;  
       if (x == 0) return 0; 
        while (y > 0) { 
            if((y & 1)==1) 
                res = (res * x) % p;
            y = y >> 1;  
            x = (x * x) % p;  
        } 
        return res; 
    }     
    
    	public static void main(String args[] ) throws NumberFormatException, IOException  {
			
		in = new InputReader(System.in);
	    out = new PrintWriter(System.out);
	    deb = new Debugger();
	    
	    int n = in.nextInt();
	    int m = in.nextInt();
	    String[] s = new String[n];
	    for(int i=0;i<n;i++) {
	    		s[i] = in.readString();
	    }
	    StringBuilder ans = new StringBuilder("");
	    int[] tkn  = new int[n];
	    int c=0;
	    for(int i=0;i<n;i++) {
	    		int f=0;
	    		StringBuilder x = new StringBuilder(s[i]);
	    		String xx = x.reverse().toString();
	    		for(int j=0;j<n;j++) {
	    			if(tkn[j]==0 && j!=i) {
	    				if(s[j].equals(xx)) {
	    					f=1;
	    					tkn[j]=1;
	    					c+= 2*(s[j].length());
	    					break;
	    				}
	    			}
	    		}
	    		if(f==1) {
	    			tkn[i]=1;
	    			ans.append(s[i]);
	    		}
	    }
	    int mx=0;
	    String xx="";
	    for(int i=0;i<n;i++) {
	    		if(tkn[i]==0) {
	    			int ff=0;
	    			for(int j=0;j<s[i].length()/2;j++) {
	    				if(s[i].charAt(j)!=s[i].charAt(s[i].length()-j-1)) {
	    					ff=1;
	    					break;
	    				}
	    			}
	    			if(ff==0) {
	    				mx = Math.max(mx, s[i].length());
	    				xx = s[i];
	    			}
	    		}
	    }
	    String a1 = ans.toString();
	    StringBuilder rv = ans.reverse();
	    out.println(c+mx);
	    out.println(a1+xx+rv.toString());
	    
	    out.close();
	}
		
/* TC space



 */
		
		static class InputReader
	    {
	        private final InputStream stream;
	        private final byte[] buf = new byte[8192];
	        private int curChar, snumChars;
	        private SpaceCharFilter filter;

	        public InputReader(InputStream stream)
	        {
	                this.stream = stream;
	        }

	        public int snext()
	        {
	                if (snumChars == -1)
	                        throw new InputMismatchException();
	                if (curChar >= snumChars)
	                {
	                        curChar = 0;
	                        try
	                        {
	                                snumChars = stream.read(buf);
	                        } catch (IOException e)
	                        {
	                                throw new InputMismatchException();
	                        }
	                        if (snumChars <= 0)
	                                return -1;
	                }
	                return buf[curChar++];
	        }

	        public int nextInt()
	        {
	                int c = snext();
	                while (isSpaceChar(c))
	                {
	                        c = snext();
	                }
	                int sgn = 1;
	                if (c == '-')
	                {
	                        sgn = -1;
	                        c = snext();
	                }
	                int res = 0;
	                do
	                {
	                        if (c < '0' || c > '9')
	                                throw new InputMismatchException();
	                        res *= 10;
	                        res += c - '0';
	                        c = snext();
	                } while (!isSpaceChar(c));
	                return res * sgn;
	        }

	        public long nextLong()
	        {
	                int c = snext();
	                while (isSpaceChar(c))
	                {
	                        c = snext();
	                }
	                int sgn = 1;
	                if (c == '-')
	                {
	                        sgn = -1;
	                        c = snext();
	                }
	                long res = 0;
	                do
	                {
	                        if (c < '0' || c > '9')
	                                throw new InputMismatchException();
	                        res *= 10;
	                        res += c - '0';
	                        c = snext();
	                } while (!isSpaceChar(c));
	                return res * sgn;
	        }

	        public int[] nextIntArray(int n)
	        {
	                int a[] = new int[n];
	                for (int i = 0; i < n; i++)
	                {
	                        a[i] = nextInt();
	                }
	                return a;
	        }

	        public long[] nextLongArray(int n)
	        {
	                long a[] = new long[n];
	                for (int i = 0; i < n; i++)
	                {
	                        a[i] = nextLong();
	                }
	                return a;
	        }
	        
	        public ArrayList<Integer> nextArrayList(int n){
	        			ArrayList<Integer> x = new ArrayList<Integer>();
	        			for(int i=0;i<n;i++) {
	        				int v = in.nextInt();
	        				x.add(v);
	        			}
	        			return x;
	        }

	        public String readString()
	        {
	                int c = snext();
	                while (isSpaceChar(c))
	                {
	                        c = snext();
	                }
	                StringBuilder res = new StringBuilder();
	                do
	                {
	                        res.appendCodePoint(c);
	                        c = snext();
	                } while (!isSpaceChar(c));
	                return res.toString();
	        }

	        public String nextLine()
	        {
	                int c = snext();
	                while (isSpaceChar(c))
	                        c = snext();
	                StringBuilder res = new StringBuilder();
	                do
	                {
	                        res.appendCodePoint(c);
	                        c = snext();
	                } while (!isEndOfLine(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;
	        }

	        private boolean isEndOfLine(int c)
	        {
	                return c == '\n' || c == '\r' || c == -1;
	        }

	        public interface SpaceCharFilter
	        {
	                public boolean isSpaceChar(int ch);
	        }

	    }
		
		static class Debugger{
			public void n(int x) {
				out.println(x);
			}
			
			public void a(int[] a) {
		        StringBuilder sb = new StringBuilder();
		        for(int i=0;i<a.length;i++) {
		        		sb.append(a[i]+" ");
		        }
		        out.println(sb.toString());
			}
		}
		
}


class Pairx {
	Pair a;
	int b;
	public Pairx(Pair a,int b) {
		this.a =a;
		this.b =b;
	}
	@Override
	public boolean equals(Object o) {
	    if (this == o) return true;
	    if (!(o instanceof Pairx)) return false;
	    Pairx p = (Pairx) o;
	    return  b == p.b;
	}
	public int compareTo(Pairx that) {
		return (int)(this.a.x - that.a.x);
	}
}


//Pair arr[] = new Pair[n]; 
//arr[0] = new Pair(10, 20); 
 class Pair { 
    int x; 
    int y; 
  
    // Constructor 
    public Pair(int x, int y) 
    { 
        this.x = x; 
        this.y = y; 
    } 
	@Override
	public boolean equals(Object o) {
	    if (this == o) return true;
	    if (!(o instanceof Pair)) return false;
	    Pair p = (Pair) o;
	    return x == p.x && y == p.y;
	}
} 
// class Compare { 
//	  //void return by default.
//    static Pair[] compare(Pair arr[], int n) 
//    { 
 
 		// (p1,p2) -> p1.x-p2.x Using lembda function...
 
//        // Comparator to sort the pair according to first element.
//        Arrays.sort(arr, new Comparator<Pair>() { 
//            @Override public int compare(Pair p1, Pair p2) 
//            { 
//                return p1.x - p2.x; 
//            } 
//        }); 
//        
//        return arr;
//    } 
//} 