Problem: There are n castles in the Lannister's Kingdom and some walls connect two castles, no two castles are connected by more than one wall, no wall connects a castle to itself. 

Sir Jaime Lannister has discovered that Daenerys Targaryen is going to attack his kingdom soon. Therefore he wants to defend his kingdom. He has k liters of a strange liquid. He wants to distribute that liquid among the castles, so each castle may contain some liquid (possibly zero or non-integer number of liters). After that the stability of a wall is defined as follows: if the wall connects two castles a and b, and they contain x and y liters of that liquid, respectively, then the strength of that wall is x·y.

Your task is to print the maximum possible sum of stabilities of the walls that Sir Jaime Lannister can achieve.

Input

The first line of the input contains two integers n and k (1 ≤ n ≤ 40, 1 ≤ k ≤ 1000).

Then n lines follows. The i-th of these lines contains n integers ai, 1, ai, 2, ..., ai, n (<image>). If castles i and j are connected by a wall, then ai, j = 1. Otherwise it is equal to 0.

It is guaranteed that ai, j = aj, i and ai, i = 0 for all 1 ≤ i, j ≤ n.

Output

Print the maximum possible sum of stabilities of the walls that Sir Jaime Lannister can achieve.

Your answer will be considered correct if its absolute or relative error does not exceed 10 - 6.

Namely: let's assume that your answer is a, and the answer of the jury is b. The checker program will consider your answer correct, if <image>.

Examples

Input

3 1
0 1 0
1 0 0
0 0 0


Output

0.250000000000


Input

4 4
0 1 0 1
1 0 1 0
0 1 0 1
1 0 1 0


Output

4.000000000000

Note

In the first sample, we can assign 0.5, 0.5, 0 liters of liquid to castles 1, 2, 3, respectively, to get the maximum sum (0.25).

In the second sample, we can assign 1.0, 1.0, 1.0, 1.0 liters of liquid to castles 1, 2, 3, 4, respectively, to get the maximum sum (4.0)

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
template <typename T>
bool chmax(T &m, const T &v) {
  if (v > m) return m = v, true;
  return false;
}
template <typename T>
bool chmin(T &m, const T &v) {
  if (v < m) return m = v, true;
  return false;
}
static const int HMAX32 = INT32_MAX / 2;
static const int HMIN32 = -HMAX32;
static const int64_t HMAX64 = INT64_MAX / 2;
static const int64_t HMIN64 = -HMAX64;
void fast_io() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
}
template <typename T>
struct ring_traits {
  static T zero() { return T(); }
  static T negate(const T &p) { return -p; }
  static T plus(const T &p1, const T &p2) { return p1 + p2; }
  static T minus(const T &p1, const T &p2) { return p1 - p2; }
  static T one() { return 1; }
  static T time(const T &p1, const T &p2) { return p1 * p2; }
  static void plus_assign(T &p1, const T &p2) { p1 += p2; }
  static void minus_assign(T &p1, const T &p2) { p1 -= p2; }
  static void time_assign(T &p1, const T &p2) { p1 *= p2; }
  static T inverse(const T &p) { return 1 / p; }
  static T divide(const T &p1, const T &p2) { return p1 / p2; }
  static void divide_assign(T &p1, const T &p2) { p1 /= p2; }
  static double norm(const T &p) { return std::abs(p); }
};
template <typename T, template <typename> class Ring = ring_traits>
struct matrix {
 private:
  std::vector<std::vector<T>> data;
  static Ring<T> traits;

 public:
  matrix() = default;
  matrix(int r, int c) : data(r, std::vector<T>(c, traits.zero())) {}
  static matrix scalar(int r, const T &val) {
    matrix ret(r, r);
    for (int i = 0; i < r; ++i) ret.data[i][i] = val;
    return ret;
  }
  static matrix eye(int r) { return scalar(r, traits.one()); }
  static matrix diagonal(const std::vector<T> &diag) {
    int r = (int)diag.size();
    matrix ret(r, r);
    for (int i = 0; i < r; ++i) ret.data[i][i] = diag[i];
    return ret;
  }
  void swap(matrix &that) { std::swap(data, that.data); }
  int r() const { return (int)data.size(); }
  int c() const {
    if (data.size()) return (int)data[0].size();
    return 0;
  }
  const std::vector<T> &operator[](int m) const { return data[m]; }
  std::vector<T> &operator[](int m) { return data[m]; }
  bool operator==(const matrix &that) const { return data == that.data; }
  std::vector<T> column(int n) {
    std::vector<T> ret;
    ret.reserve(r());
    for (auto &row : data) ret.push_back(row[n]);
  }
  void resize(int new_m, int new_n) {
    T zero = traits.zero();
    data.resize(new_m);
    for (auto &row : data) row.resize(new_n);
  }
  matrix &negate() {
    for (auto &row : data)
      for (T &ele : row) ele = traits.negate(ele);
    return *this;
  }
  matrix operator-() const { return matrix(*this).negate(); }
  matrix &operator+=(const T &scalar) {
    for (auto &row : data)
      for (T &ele : row) traits.plus_assign(ele, scalar);
    return *this;
  }
  matrix &operator+(const T &scalar) const {
    matrix ret(*this);
    return ret += scalar;
  }
  matrix &operator-=(const T &scalar) {
    for (auto &row : data)
      for (T &ele : row) traits.minus_assign(ele, scalar);
    return *this;
  }
  matrix &operator-(const T &scalar) const {
    matrix ret(*this);
    return ret -= scalar;
  }
  matrix &operator*=(const T &scalar) {
    for (auto &row : data)
      for (T &ele : row) traits.time_assign(ele, scalar);
    return *this;
  }
  matrix &operator*(const T &scalar) const {
    matrix ret(*this);
    return ret *= scalar;
  }
  matrix &operator/=(const T &scalar) {
    for (auto &row : data)
      for (T &ele : row) traits.divide_assign(ele, scalar);
    return *this;
  }
  matrix &operator/(const T &scalar) const {
    matrix ret(*this);
    return ret /= scalar;
  }
  matrix &operator+=(const matrix &that) {
    int rr = r(), cc = c();
    if (rr != that.r() || cc != that.c()) throw 0;
    for (int i = 0; i < rr; ++i) {
      for (int j = 0; j < cc; ++j) {
        traits.plus_assign(data[i][j], that.data[i][j]);
      }
    }
    return *this;
  }
  matrix &operator+(const matrix &that) const {
    matrix ret(*this);
    return ret += that;
  }
  matrix &operator-=(const matrix &that) {
    int rr = r(), cc = c();
    if (rr != that.r() || cc != that.c()) throw 0;
    for (int i = 0; i < rr; ++i) {
      for (int j = 0; j < cc; ++j) {
        traits.minus_assign(data[i][j], that.data[i][j]);
      }
    }
    return *this;
  }
  matrix &operator-(const matrix &that) const {
    matrix ret(*this);
    return ret -= that;
  }
  matrix operator*(const matrix &that) const {
    int mm = r(), nn = c(), pp = that.c();
    const matrix &self = *this;
    if (nn != that.r()) throw 0;
    matrix ret(mm, pp);
    for (int i = 0; i < mm; ++i) {
      for (int j = 0; j < pp; ++j) {
        T acc = traits.zero();
        for (int k = 0; k < nn; ++k)
          traits.plus_assign(acc,
                             traits.time(self.data[i][k], that.data[k][j]));
        ret.data[i][j] = acc;
      }
    }
    return ret;
  }
  matrix &operator*=(const matrix &that) { return *this = *this * that; }
};
template <typename T, template <typename> class Ring>
matrix<T, Ring> operator+(const T &value, const matrix<T, Ring> &p1) {
  matrix<T, Ring> ret(p1);
  return ret += value;
}
template <typename T, template <typename> class Ring>
matrix<T, Ring> operator*(const T &value, const matrix<T, Ring> &p1) {
  matrix<T, Ring> ret(p1);
  return ret *= value;
}
template <typename T, template <typename> class Ring>
matrix<T, Ring> operator-(const T &value, const matrix<T, Ring> &p1) {
  matrix<T, Ring> ret(p1);
  return ret.negate() += value;
}
template <typename T, template <typename> class Ring>
void swap(matrix<T, Ring> &p1, matrix<T, Ring> &p2) {
  p1.swap(p2);
}
template <typename T, template <typename> class Ring = ring_traits>
matrix<T, Ring> permutation_matrix(const std::vector<int> &p) {
  int n = (int)p.size();
  Ring<T> traits;
  matrix<T, Ring> P(n, n);
  for (int i = 0; i < n; ++i) P[i][p[i]] = traits.one();
  return P;
}
template <typename T, template <typename> class Ring>
int LU_decompose(const matrix<T, Ring> &A, matrix<T, Ring> &L,
                 matrix<T, Ring> &U) {
  int n = A.r();
  Ring<T> traits;
  if (n != A.c()) throw 0;
  L = matrix<T, Ring>::eye(n);
  U = A;
  for (int j = 0; j < n; ++j) {
    if (U[j][j] == traits.zero()) return -1;
    for (int i = j + 1; i < n; ++i) {
      T lij = traits.divide(U[i][j], U[j][j]);
      L[i][j] = lij;
      U[i][j] = 0;
      for (int k = j + 1; k < n; ++k)
        traits.minus_assign(U[i][k], U[j][k] * lij);
    }
  }
  return 0;
}
template <typename T, template <typename> class Ring>
int PLU_decompose(const matrix<T, Ring> &A, std::vector<int> &p,
                  matrix<T, Ring> &L, matrix<T, Ring> &U, bool &positive) {
  int n = A.r();
  Ring<T> traits;
  if (n != A.c()) throw 0;
  positive = true;
  U = A;
  L = matrix<T, Ring>(n, n);
  p = std::vector<int>(n);
  for (int i = 0; i < n; ++i) p[i] = i;
  for (int j = 0; j < n; ++j) {
    double max_norm = traits.norm(U[j][j]);
    int max_index = j;
    for (int jj = j + 1; jj < n; ++jj) {
      double cur_norm = traits.norm(U[jj][j]);
      if (cur_norm > max_norm) {
        max_norm = cur_norm;
        max_index = jj;
      }
    }
    if (U[max_index][j] == traits.zero()) return -1;
    if (j != max_index) {
      std::swap(U[j], U[max_index]);
      std::swap(L[j], L[max_index]);
      std::swap(p[j], p[max_index]);
      positive = !positive;
    }
    for (int i = j + 1; i < n; ++i) {
      T lij = traits.divide(U[i][j], U[j][j]);
      L[i][j] = lij;
      U[i][j] = 0;
      for (int k = j + 1; k < n; ++k)
        traits.minus_assign(U[i][k], U[j][k] * lij);
    }
  }
  for (int i = 0; i < n; ++i) L[i][i] = 1;
  return 0;
}
template <typename T, template <typename> class Ring>
T determinant(const matrix<T, Ring> &A) {
  Ring<T> traits;
  std::vector<int> p;
  bool pos;
  matrix<T, Ring> L, U;
  if (PLU_decompose(A, p, L, U, pos) < 0) return traits.zero();
  T ret = traits.one();
  for (int i = 0; i < A.r(); ++i) traits.time_assign(ret, U[i][i]);
  if (!pos) ret = traits.negate(ret);
  return ret;
}
struct max_clique {
  static const int maxn = 41;
  vector<int> found;
  bool g[maxn][maxn] = {};
  int maxc[maxn];
  bool dfs(vector<int> &clique, const vector<int> &todo) {
    if (todo.empty()) {
      if (clique.size() > found.size()) {
        found = clique;
        return true;
      }
    } else {
      for (int i = 0; i < (int)todo.size(); ++i) {
        if (clique.size() + todo.size() - i <= found.size()) continue;
        int v = todo[i];
        if (clique.size() + maxc[v] <= found.size()) continue;
        vector<int> next;
        for (int j = i + 1; j < (int)todo.size(); ++j) {
          int w = todo[j];
          if (g[v][w]) next.push_back(w);
        }
        clique.push_back(v);
        if (dfs(clique, next)) return true;
        clique.pop_back();
      }
    }
    return false;
  }
  int solve() {
    for (int u = maxn - 1; u >= 0; --u) {
      vector<int> clique = {u};
      vector<int> todo;
      for (int v = 0; v < maxn; ++v)
        if (g[u][v]) todo.push_back(v);
      dfs(clique, todo);
      maxc[u] = (int)found.size();
    }
    return (int)found.size();
  }
};
int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  max_clique mc;
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j) {
      int t;
      scanf("%d", &t);
      mc.g[i][j] = t;
    }
  int m = mc.solve();
  ;
  printf("%.10lf\n", 1.0 * k * k * (m - 1) / 2 / m);
  return 0;
}