max clique

#include <bits/stdc++.h>
// tiom4eg's precompiler options
// POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS
// IO settings
#define fastIO ios_base::sync_with_stdio(false); cin.tie(0)
// Quick types
#define ll long long
#define ld double
#define ull unsigned long long
#define pii pair <int, int>
#define pll pair <ll, ll>
#define vi vector <int>
#define mi vector <vector <int> >
// Quick functions
#define endl "\n"
#define F first
#define S second
#define all(a) a.begin(), a.end()
#define sz(a) a.size()
#define pb push_back
#define mp make_pair
#define min(a, b) ((a < b) ? (a) : (b))
#define max(a, b) ((a > b) ? (a) : (b))
// Quick fors
#define FOR(i, a, b) for (int i = a; i < b; ++i)
#define RFOR(i, a, b) for (int i = a; i >= b; --i)
// Pragmas
#pragma GCC optimize("O3,unroll-loops") // let the chaos begin!
//#pragma GCC target("avx,avx2,bmi,bmi2,popcnt,lzcnt,tune=native")
#pragma GCC comment(linker, "/stack:200000000")
// PBDS
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ordered_set tree <int, null_type, less <int>, rb_tree_tag, tree_order_statistics_node_update>
#define ook order_of_key
#define fbo find_by_order
// POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS POGGERS
using namespace std;
using namespace __gnu_pbds;
mt19937 rng(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count());
#define int long long

signed main() {
    srand(rng());
    fastIO;
    cout << fixed << setprecision(9);
    int n, k; cin >> n >> k;
    vi adj(n);
    FOR(i, 0, n) FOR(j, 0, n) {
        int x; cin >> x;
        adj[i] |= (x << j);
    }
    vi p(n); FOR(i, 0, n) p[i] = i;
    int best = 0;
    FOR(iter, 0, 100000) {
        random_shuffle(all(p));
        int cur = 0, mask = (1LL << n) - 1;
        FOR(i, 0, n) if ((mask >> p[i]) & 1) cur++, mask &= adj[p[i]];
        best = max(best, cur);
    }
    cout << 0.5 * k * k * (best - 1) / best;
}