#include <bits/stdc++.h>
using namespace std;
const int maxn = 100010;
const int mod = 1e9 + 7;
const double eps = 1e-6;
const double PI = acos(-1);
template <typename T>
inline void read(T &x) {
  x = 0;
  T f = 1;
  char ch;
  do {
    ch = getchar();
    if (ch == '-') f = -1;
  } while (ch < '0' || ch > '9');
  do x = x * 10 + ch - '0', ch = getchar();
  while (ch <= '9' && ch >= '0');
  x *= f;
}
template <typename A, typename B>
inline void read(A &x, B &y) {
  read(x);
  read(y);
}
template <typename A, typename B, typename C>
inline void read(A &x, B &y, C &z) {
  read(x);
  read(y);
  read(z);
}
template <typename A, typename B, typename C, typename D>
inline void read(A &x, B &y, C &z, D &w) {
  read(x);
  read(y);
  read(z);
  read(w);
}
template <typename A, typename B>
inline A fexp(A x, B p) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mod)
    if (p & 1) ans = 1LL * ans * x % mod;
  return ans;
}
template <typename A, typename B>
inline A fexp(A x, B p, A mo) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mo)
    if (p & 1) ans = 1LL * ans * x % mo;
  return ans;
}
long long has[55];
int n, K, Ans;
void dfs(long long R, long long P, long long X, int ans) {
  if (P == 0 && X == 0) {
    Ans = max(Ans, ans);
    return;
  }
  int mx = n + 1, mw = 0;
  for (int i = 1; i <= n; i++)
    if ((1LL << i) & (P | X)) {
      long long t = P & ((1LL << i) | has[i]);
      int nm = 0;
      for (int j = 1; j <= n; j++)
        if ((1LL << j) & t) nm++;
      if (nm < mx) {
        mx = nm;
        mw = i;
      }
    }
  long long t = P & ((1LL << mw) | has[mw]);
  for (int j = 1; j <= n; j++)
    if ((1LL << j) & t) {
      dfs(P | (1LL << j), P - (P & ((1LL << j) | has[j])),
          X - (X & ((1LL << j) | has[j])), ans + 1);
      if ((1LL << j) & P) P -= 1LL << j;
      if ((1LL << j) & X) X -= 1LL << j;
    }
}
void Work() {
  dfs(0, (1LL << n + 1) - 2, 0, 0);
  double ans = (double)K / Ans;
  ans *= ans;
  ans *= 1LL * Ans * (Ans - 1) / 2;
  printf("%.18lf\n", ans);
}
void Init() {
  read(n, K);
  for (int i = (1); i <= (n); i++)
    for (int j = (1); j <= (n); j++) {
      int x;
      read(x);
      if (!x) has[i] |= 1LL << j;
    }
}
int main() {
  Init();
  Work();
  return 0;
}
