#include <bits/stdc++.h>
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target( \
    "sse,sse2,sse3,ssse3,sse4,sse4.2,popcnt,abm,mmx,avx,tune=native")
using namespace std;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cout << name << " : " << arg1 << std::endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
const int N = 45;
const int MAX = 2e6 + 5;
const int MOD = 1000000007;
int n, k, maxclique;
int G[N][N];
int dp[1 << 22];
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  srand(time(NULL));
  cout << fixed << setprecision(10);
  clock_t clk;
  clk = clock();
  ;
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> G[i][j];
    }
    G[i][i] = 1;
  }
  int x = n / 2;
  int y = n - x;
  vector<int> bits;
  for (int msk = 0; msk < (1 << x); msk++) {
    bits.clear();
    for (int i = 0; i < x; i++)
      if (msk & (1 << i)) bits.push_back(i);
    int ok = 1, sz = bits.size();
    for (int i : bits)
      for (int j : bits)
        if (!G[i][j]) ok = 0;
    if (ok)
      dp[msk] = sz;
    else
      for (int i : bits) dp[msk] = max(dp[msk], dp[msk ^ (1 << i)]);
    maxclique = max(maxclique, dp[msk]);
  }
  for (int msk = 0; msk < (1 << y); msk++) {
    bits.clear();
    for (int i = 0; i < y; i++)
      if (msk & (1 << i)) bits.push_back(i + x);
    int ok = 1, sz = bits.size();
    for (int i : bits)
      for (int j : bits)
        if (!G[i][j]) ok = 0;
    if (!ok) continue;
    int _msk = 0;
    for (int j = 0; j < x; j++) {
      int ok = 1;
      for (int i : bits)
        if (!G[i][j]) ok = 0;
      if (ok) _msk |= (1 << j);
    }
    maxclique = max(maxclique, sz + dp[_msk]);
  }
  double ans = 0.5 * k * k * (maxclique - 1) / maxclique;
  cout << ans << "\n";
  clk = clock() - clk;
  cerr << fixed << setprecision(6) << "Time: " << ((double)clk) / CLOCKS_PER_SEC
       << "\n";
  return 0;
  ;
}
