import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.PrintStream;
import java.util.Arrays;
import java.util.Random;
import java.io.IOException;
import java.io.Reader;
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author tanzaku
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        MyInput in = new MyInput(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskE solver = new TaskE();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskE {
        int n;
        int k;
        long[] neigibor;
        Random random = new Random();
        long maxClique;

        public void solve(int testNumber, MyInput in, PrintWriter out) {
            n = in.nextInt();
            k = in.nextInt();
            neigibor = new long[n];
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < n; j++) {
                    neigibor[i] |= in.nextLong() << j;
                }
            }
            long maxClique = bronKerbosch();
            long a = Long.bitCount(maxClique);
            dump(a);
            out.printf("%.12f\n", a * (a - 1.0) / 2 * k / a * k / a);
        }

        static void dump(Object... o) {
            System.err.println(Arrays.deepToString(o));
        }

        long bronKerbosch() {
            maxClique = 0;
            bronKerbosch2(0, (1L << n) - 1, 0);
            return maxClique;
        }

        void bronKerbosch2(long r, long p, long x) {
//        if (Long.bitCount(maxClique) >= Long.bitCount(r|p|x)) return;
            long px = p | x;
            if (px == 0) {
                if (Long.bitCount(maxClique) < Long.bitCount(r)) {
                    maxClique = r;
                }
                return;
            }
            int cnt = Long.bitCount(px);
            int choice = random.nextInt(cnt);
            int u;
            for (int i = 0; ; i++) {
                if ((px >>> i & 1) != 0 && choice-- == 0) {
                    u = i;
                    break;
                }
            }
//        dump(r, p, x, u, neigibor);
            long ne = p & ~neigibor[u];
            for (int v = 0; v < n; v++)
                if ((ne >>> v & 1) != 0) {
                    bronKerbosch2(r | 1L << v, p & neigibor[v], x & neigibor[v]);
                    p &= ~(1L << v);
                    x |= 1L << v;
                }
        }

    }

    static class MyInput {
        private final BufferedReader in;
        private static int pos;
        private static int readLen;
        private static final char[] buffer = new char[1024 * 8];
        private static char[] str = new char[500 * 8 * 2];
        private static boolean[] isDigit = new boolean[256];
        private static boolean[] isSpace = new boolean[256];
        private static boolean[] isLineSep = new boolean[256];

        static {
            for (int i = 0; i < 10; i++) {
                isDigit['0' + i] = true;
            }
            isDigit['-'] = true;
            isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true;
            isLineSep['\r'] = isLineSep['\n'] = true;
        }

        public MyInput(InputStream is) {
            in = new BufferedReader(new InputStreamReader(is));
        }

        public int read() {
            if (pos >= readLen) {
                pos = 0;
                try {
                    readLen = in.read(buffer);
                } catch (IOException e) {
                    throw new RuntimeException();
                }
                if (readLen <= 0) {
                    throw new MyInput.EndOfFileRuntimeException();
                }
            }
            return buffer[pos++];
        }

        public int nextInt() {
            int len = 0;
            str[len++] = nextChar();
            len = reads(len, isSpace);
            int i = 0;
            int ret = 0;
            if (str[0] == '-') {
                i = 1;
            }
            for (; i < len; i++) ret = ret * 10 + str[i] - '0';
            if (str[0] == '-') {
                ret = -ret;
            }
            return ret;
        }

        public long nextLong() {
            int len = 0;
            str[len++] = nextChar();
            len = reads(len, isSpace);
            int i = 0;
            long ret = 0;
            if (str[0] == '-') {
                i = 1;
            }
            for (; i < len; i++) ret = ret * 10 + str[i] - '0';
            if (str[0] == '-') {
                ret = -ret;
            }
            return ret;
        }

        public char nextChar() {
            while (true) {
                final int c = read();
                if (!isSpace[c]) {
                    return (char) c;
                }
            }
        }

        int reads(int len, boolean[] accept) {
            try {
                while (true) {
                    final int c = read();
                    if (accept[c]) {
                        break;
                    }
                    if (str.length == len) {
                        char[] rep = new char[str.length * 3 / 2];
                        System.arraycopy(str, 0, rep, 0, str.length);
                        str = rep;
                    }
                    str[len++] = (char) c;
                }
            } catch (MyInput.EndOfFileRuntimeException e) {
            }
            return len;
        }

        static class EndOfFileRuntimeException extends RuntimeException {
        }

    }
}

