// This Code was made by Chinese_zjc_.
#include <bits/stdc++.h>
// #define debug
const double eps = 1e-8;
int n;
double w[10][10], a[10][10], b[10], c[10], ans;
double solve(int n, int w[10][10])
{
    std::memset(a, 0, sizeof(a));
    for (int i = 1; i != n; ++i)
    {
        b[i] = -w[0][i];
        for (int j = 1; j != n; ++j)
            a[i][j] -= w[0][j];
        for (int j = 1; j != n; ++j)
            a[i][j] -= w[0][i];
        for (int j = 1; j != n; ++j)
            a[i][j] += w[i][j];
    }
    // for (int i = 1; i != n; ++i)
    // {
    //     for (int j = 1; j != n; ++j)
    //         std::cout << a[i][j] << ' ';
    //     std::cout << b[i] << std::endl;
    // }
    for (int i = 1; i != n; ++i)
    {
        for (int j = i; j != n; ++j)
            if (std::abs(a[i][j]) > eps)
            {
                std::swap(a[i], a[j]);
                std::swap(b[i], b[j]);
                break;
            }
        double v = 1.0 / a[i][i];
        for (int j = 0; j != n; ++j)
            a[i][j] *= v;
        b[i] *= v;
        for (int j = 0; j != n; ++j)
            if (i != j)
            {
                v = a[j][i];
                for (int k = 0; k != n; ++k)
                    a[j][k] -= v * a[i][k];
                b[j] -= v * b[i];
            }
    }
    for (int i = 1; i != n; ++i)
        c[i] = b[i] / a[i][i];
    c[0] = 1 - std::accumulate(c + 1, c + n, 0.0);
    double res = 0;
    for (int i = 0; i != n; ++i)
        for (int j = 0; j != i; ++j)
            res += c[i] * c[j] * w[i][j];
    // for (int i = 0; i != n; ++i)
    //     std::cout << c[i] << " \n"[i + 1 == n];
    for (int i = 0; i != n; ++i)
        if (c[i] < 0)
            return 0;
    return res;
}
signed main()
{
    std::ios::sync_with_stdio(false);
    std::cin >> n;
    for (int i = 0; i != n; ++i)
        for (int j = 0; j != n; ++j)
            std::cin >> w[i][j];
    for (int i = 1; i != 1 << n; ++i)
    {
        int id[10], cnt = 0;
        for (int j = 0; j != n; ++j)
            if (i >> j & 1)
                id[cnt++] = j;
        int v[10][10];
        std::memset(v, 0, sizeof(v));
        for (int j = 0; j != cnt; ++j)
            for (int k = 0; k != cnt; ++k)
                v[j][k] = w[id[j]][id[k]];
        ans = std::max(ans, solve(cnt, v));
    }
    std::cout << std::fixed << std::setprecision(10) << ans << std::endl;
    return 0;
}