#include <bits/stdc++.h>

using i64 = long long;
using namespace std;

const int N = 15;

bool vis[N];

double ans[N];

bool gauss(vector<vector<double>>& a) {
    int n = a.size();
    // for (int i = 0; i < n; i++) {
    //     for (int j = 0; j <= n; j++) {
    //         cout << a[i][j] << " ";
    //     }
    //     cout << "\n";
    // }
    for (int i = 0; i < n; i++) {
        if (!vis[i]) continue;
        int p = -1;
        for (int j = i; j < n; j++) {
            if (!vis[j]) continue;
            if (p == -1 || abs(a[j][i]) > abs(a[p][i])) p = j;
        }
        if (p == -1) return 0;
        if (i != p) swap(a[p], a[i]);
        for (int j = i + 1; j < n; j++) {
            for (int k = i + 1; k <= n; k++) {
                a[j][k] -= a[j][i] / a[i][i] * a[i][k]; 
            }
            a[j][i] = 0;
        }
    }
    // for (int i = 0; i < n; i++) {
    //     for (int j = 0; j <= n; j++) {
    //         cout << a[i][j] << " ";
    //     }
    //     cout << "\n";
    // }
    for (int i = n - 1; i >= 0; i--) {
        if (!vis[i]) continue;
        for (int j = 0; j < i; j++) {
            if (!vis[j]) continue;
            // cout << "i = " << i << " j = " << j << " " << a[j][n] << " " << a[i][n] << " " << a[j][i] << " " << a[i][i] << "\n";
            a[j][n] -= a[i][n] * a[j][i] / a[i][i];
            a[j][i] = 0;
        }
    }
    // for (int i = 0; i < n; i++) {
    //     for (int j = 0; j <= n; j++) {
    //         cout << a[i][j] << " ";
    //     }
    //     cout << "\n";
    // }
    for (int i = 0; i < n - 1; i++) {
        if (!vis[i]) {
            ans[i] = 0;
        } else {
            ans[i] = a[i][n] / a[i][i];
            if (ans[i] < 0) return 0;
        }
    }
    return 1;
}

int n;
int a[N][N];

double solve(int ms) {
    for (int i = 0; i < n; i++) {
        vis[i] = ms >> i & 1;
    }
    vector coef(n + 1, vector<double>(n + 2, 0));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (vis[j]) {
                coef[i][j] = a[i][j];
            }
        }
        coef[i][n] = 1, coef[i][n + 1] = 0;
    }
    for (int i = 0; i < n; i++) {
        coef[n][i] = vis[i];
    }
    vis[n] = 1;
    coef[n][n] = 0, coef[n][n + 1] = 1;
    // cout << "mask = " << ms << " ========= \n";
    // for (int i = 0; i <= n; i++) {
    //     for (int j = 0; j <= n + 1; j++) {
    //         cout << coef[i][j] << " ";
    //     }
    //     cout << "\n";
    // }
    if (gauss(coef)) {
        double tmp = 0;
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                tmp += ans[i] * ans[j] * a[i][j];
            }
        }
        return tmp;
    }
    return 0;
}

int main() {
    cout << fixed << setprecision(6);
    cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> a[i][j];
        }
    }
    double res = 0;
    for (int ms = 0; ms < (1 << n); ms++) {
        res = max(res, solve(ms));
    }
    cout << res << "\n";
}