source_code: 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 {
          }
  
      }
  }
  
  