#include <bits/stdc++.h>
using namespace std;
int adj[42][42];
int dp[1 << 21];
int c1[42], c2[42], c3[43];
int max_count;
int n1, n2, n;
int count_bit(int b) {
  int c = 0;
  for (int i = b; i; i -= (i & -i)) c++;
  return c;
}
int main() {
  int k, v;
  scanf("%d %d", &n, &k);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      scanf("%d", &adj[i][j]);
    }
    adj[i][i] = 1;
  }
  n1 = n / 2;
  n2 = n - n1;
  for (int i = 0; i < n2; i++) dp[1 << i] = 1;
  for (int i = 0; i < n1; i++) {
    for (int j = 0; j < n1; j++) {
      c1[i] |= (adj[i][j] << j);
    }
  }
  for (int i = n1; i < n; i++) {
    for (int j = n1; j < n; j++) {
      c2[i - n1] |= (adj[i][j] << (j - n1));
    }
  }
  for (int i = 0; i < n1; i++) {
    for (int j = n1; j < n; j++) {
      c3[i] |= (adj[i][j] << (j - n1));
    }
  }
  for (int i = 1; i < (1 << n2); i++) {
    int rb = (1 << 23) - 1;
    for (int j = 0; (1 << j) <= i; j++) {
      if (i & (1 << j)) {
        rb &= c2[j];
      }
    }
    if ((rb & i) == i) {
      int res = count_bit(i);
      dp[i] = res;
      max_count = max(max_count, res);
    } else {
      for (int j = 0; j < n2; j++) {
        dp[i] = max(dp[i], dp[i & ~(1 << j)]);
      }
    }
  }
  for (int i = 1; i < (1 << n1); i++) {
    int rb = (1 << 23) - 1;
    for (int j = 0; (1 << j) <= i; j++) {
      if (i & (1 << j)) {
        rb &= c1[j];
      }
    }
    if ((rb & i) == i) {
      int lb = (1 << 23) - 1;
      for (int j = 0; (1 << j) <= i; j++) {
        if (i & (1 << j)) {
          lb &= c3[j];
        }
      }
      int res = count_bit(i) + dp[lb];
      max_count = max(max_count, res);
    }
  }
  printf("%.7lf\n", k * k * (max_count - 1) / (2.0 * max_count));
}
