#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const long long INFF = 0x3f3f3f3f3f3f3f3fll;
const long long M = 1e9 + 7;
const long long maxn = 50 + 7;
const double eps = 0.00000001;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
template <typename T>
inline T abs(T a) {
  return a > 0 ? a : -a;
}
template <typename T>
inline T powMM(T a, T b) {
  T ret = 1;
  for (; b; b >>= 1ll, a = a * a % M)
    if (b & 1) ret = 1ll * ret * a % M;
  return ret;
}
int n;
int ans;
int edge[maxn][maxn], cnt[maxn], vis[maxn];
bool dfs(int u, int pos) {
  int i, j;
  for (i = u + 1; i <= n; i++) {
    if (cnt[i] + pos <= ans) return 0;
    if (edge[u][i]) {
      for (j = 0; j < pos; j++)
        if (!edge[i][vis[j]]) break;
      if (j == pos) {
        vis[pos] = i;
        if (dfs(i, pos + 1)) return 1;
      }
    }
  }
  if (pos > ans) {
    ans = pos;
    return 1;
  }
  return 0;
}
int maxclique() {
  int i;
  ans = -1;
  for (i = n; i >= 1; i--) {
    vis[0] = i;
    dfs(i, 1);
    cnt[i] = ans;
  }
  return ans;
}
int main() {
  int k;
  int i, j;
  scanf("%d%d", &n, &k);
  for (i = 1; i <= n; i++)
    for (j = 1; j <= n; j++) scanf("%d", &edge[i][j]);
  maxclique();
  printf("%.16lf", 0.5 * k * k * (ans - 1) / ans);
}
