source_code: import java.io.IOException;
  import java.io.InputStream;
  import java.util.*;
  
  public class E {
  	
  	static InputStream is;
  	//String INPUT = "";
  
  	public static void main(String[] args) throws IOException {
  		is = System.in;
  		int n = ni();
  		int k = ni();
  		
  		int[][] aj = new int[n][n];
  		
  		for (int i = 0; i < aj.length; i++) {
  			aj[i] = na(n);
  		}
  		
  		int F = (n+1)/2;
  		int B = n-F;
  		
  		int[] spanftf = new int[F];
  		int[] spanftb = new int[F];
  		for(int i =0; i < F; i++){
  			for(int j =0; j < F; j++){
  				if(i == j || aj[i][j] == 1){
  					spanftf[i] |= 1<<j;
  				}
  			}
  			for(int j =0; j< B; j++){
  				if(aj[i][F+j] == 1){
  					spanftb[i] |= 1<<j;
  				}
  			}
  		}
  		int[] maxes = new int[1<<B];
  		for(int bm = 0; bm < (1<<F); bm++){
  			int anded = (1<<F)-1;
  			int spanToBack = (1<<B)-1;
  			
  			for(int i =0; i < F; i++){
  				if((1<<i & bm) != 0){
  					anded &= spanftf[i];
  					spanToBack &= spanftb[i];
  				}
  			}
  			
  			if((anded & bm) == bm){
  				maxes[spanToBack] = Math.max(maxes[spanToBack], Integer.bitCount(bm));
  			}
  		}
  		int[] spanbtb = new int[B];
  		for(int i =0; i < B; i++){
  			for(int j =0; j< B; j++){
  				if(aj[F+i][F+j] == 1 || i == j){
  					spanbtb[i] |= 1<<j;
  				}
  			}
  		}
  		boolean[] isgood = new boolean[1<<B];
  		for(int bm =0; bm < (1<<B); bm++){
  			int anded = (1<<B)-1;
  			
  			for(int i =0; i < B; i++){
  				if((1<<i & bm) != 0){
  					anded &= spanbtb[i];
  				}
  			}
  			
  			if((anded & bm) == bm){
  				isgood[bm] = true;
  			}
  			
  		}
  		bybc[] tosort = new bybc[1<<B];
  		for (int i = 0; i < tosort.length; i++) {
  			tosort[i]= new bybc(i);
  		}
  		Arrays.sort(tosort);
  		
  		int best = 1;
  		for (int i = 0; i < tosort.length; i++) {
  			int at  =tosort[i].mask;
  			if(isgood[at]){
  				best = Math.max(best, maxes[at]+Integer.bitCount(at));
  			}
  			
  			for(int j =0; j < B; j++){
  				if((1<<j & at) != 0){
  					int to = at - (1<<j);
  					maxes[to] = Math.max(maxes[to], maxes[at]);
  				}
  			}
  			
  		}
  		
  		//System.out.println("best: " + best);
  		
  		double ans= best*(best-1)/2.0 * (k*k/(double)(best*best));
  		System.out.println(ans);
  	}
  	
  	static class bybc implements Comparable<bybc>{
  		int mask;
  
  		public bybc(int mask) {
  			super();
  			this.mask = mask;
  		}
  		
  		@Override
  		public int compareTo(bybc o) {
  			return Integer.bitCount(o.mask) - Integer.bitCount(mask);
  		}
  	}
  	
  	private static byte[] inbuf = new byte[1024];
  	public static int lenbuf = 0, ptrbuf = 0;
  	
  	private static int readByte()
  	{
  		if(lenbuf == -1)throw new InputMismatchException();
  		if(ptrbuf >= lenbuf){
  			ptrbuf = 0;
  			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
  			if(lenbuf <= 0)return -1;
  		}
  		return inbuf[ptrbuf++];
  	}
  	
  	private static boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
  	private static int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
  	
  	private static double nd() { return Double.parseDouble(ns()); }
  	private static char nc() { return (char)skip(); }
  	
  	private static String ns()
  	{
  		int b = skip();
  		StringBuilder sb = new StringBuilder();
  		while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
  			sb.appendCodePoint(b);
  			b = readByte();
  		}
  		return sb.toString();
  	}
  	
  	private static char[] ns(int n)
  	{
  		char[] buf = new char[n];
  		int b = skip(), p = 0;
  		while(p < n && !(isSpaceChar(b))){
  			buf[p++] = (char)b;
  			b = readByte();
  		}
  		return n == p ? buf : Arrays.copyOf(buf, p);
  	}
  	
  	private static char[][] nm(int n, int m)
  	{
  		char[][] map = new char[n][];
  		for(int i = 0;i < n;i++)map[i] = ns(m);
  		return map;
  	}
  	
  	private static int[] na(int n)
  	{
  		int[] a = new int[n];
  		for(int i = 0;i < n;i++)a[i] = ni();
  		return a;
  	}
  	
  	private static int ni()
  	{
  		int num = 0, b;
  		boolean minus = false;
  		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
  		if(b == '-'){
  			minus = true;
  			b = readByte();
  		}
  		
  		while(true){
  			if(b >= '0' && b <= '9'){
  				num = num * 10 + (b - '0');
  			}else{
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  	
  	private static long nl()
  	{
  		long num = 0;
  		int b;
  		boolean minus = false;
  		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
  		if(b == '-'){
  			minus = true;
  			b = readByte();
  		}
  		
  		while(true){
  			if(b >= '0' && b <= '9'){
  				num = num * 10 + (b - '0');
  			}else{
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  	
  	//private boolean oj = System.getProperty("ONLINE_JUDGE") != null;
  	//private void tr(Object... o) { if(!oj)System.out.println(Arrays.deepToString(o)); }
  }