source_code: import java.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.io.PrintWriter;
  import java.io.BufferedWriter;
  import java.io.Writer;
  import java.io.OutputStreamWriter;
  import java.util.InputMismatchException;
  import java.io.IOException;
  import java.io.InputStream;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   *
   * @author Rustam Musin (PloadyFree@gmail.com)
   */
  public class Main {
      public static void main(String[] args) {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          InputReader in = new InputReader(inputStream);
          OutputWriter out = new OutputWriter(outputStream);
          TaskE solver = new TaskE();
          solver.solve(1, in, out);
          out.close();
      }
  
      static class TaskE {
          int n;
          double k;
          boolean[][] g;
  
          public void solve(int testNumber, InputReader in, OutputWriter out) {
              n = in.readInt();
              k = in.readInt();
  
              g = new boolean[n][n];
              for (int i = 0; i < n; i++) {
                  for (int j = 0; j < n; j++) {
                      g[i][j] = in.readInt() == 1;
                  }
              }
  
              double answer = solve();
              out.printFormat("%.20f", answer);
          }
  
          private double solve() {
              int firstPartSize = g.length / 2;
              int secondPartSize = g.length - firstPartSize;
  
              int[] firstPart = findMaxCliqueSize(firstPartSize);
  
              int m1Full = (1 << firstPartSize) - 1;
              int maxCliqueSize = 1;
              for (int m = 0; m < 1 << secondPartSize; m++) {
                  if (isClique(secondPartSize, m, firstPartSize)) {
                      int m1 = m1Full;
                      for (int j = 0; j < secondPartSize; j++) {
                          if (bit(m, j)) {
                              for (int i = 0; i < firstPartSize; i++) {
                                  if (bit(m1, i) && !g[i][j + firstPartSize]) {
                                      m1 ^= 1 << i;
                                  }
                              }
                          }
                      }
                      int firstCliqueSize = firstPart[m1];
                      int secondCliqueSize = Integer.bitCount(m);
                      int curCliqueSize = firstCliqueSize + secondCliqueSize;
                      if (curCliqueSize > maxCliqueSize) {
                          maxCliqueSize = curCliqueSize;
                      }
                  }
              }
  
              return k * k * (maxCliqueSize - 1) / (2 * maxCliqueSize);
          }
  
          private int[] findMaxCliqueSize(int size) {
              int[] dp = new int[1 << size];
              for (int m = 1; m < 1 << size; m++) {
                  if (isClique(size, m, 0)) {
                      dp[m] = Integer.bitCount(m);
                  }
              }
              for (int m = 1; m < 1 << size; m++) {
                  for (int i = 0; i < size; i++) {
                      if ((m >> i & 1) == 0) {
                          dp[m | (1 << i)] = Math.max(dp[m | (1 << i)], dp[m]);
                      }
                  }
              }
              return dp;
          }
  
          private boolean isClique(int size, int m, int offset) {
              for (int i = 0; i < size; i++) {
                  if (bit(m, i)) {
                      for (int j = i + 1; j < size; j++) {
                          if (bit(m, j) && !g[i + offset][j + offset]) {
                              return false;
                          }
                      }
                  }
              }
              return true;
          }
  
          private boolean bit(int m, int b) {
              return (m >> b & 1) != 0;
          }
  
      }
  
      static class InputReader {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          private InputReader.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 boolean isSpaceChar(int c) {
              if (filter != null) {
                  return filter.isSpaceChar(c);
              }
              return isWhitespace(c);
          }
  
          public static boolean isWhitespace(int c) {
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
          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 printFormat(String format, Object... objects) {
              writer.printf(format, objects);
          }
  
          public void close() {
              writer.close();
          }
  
      }
  }
  
  