#include <bits/stdc++.h>
#define rep(i, l, r) for (int i = l; i <= r; i++)
using namespace std;
const int N = 15;

struct solver {
    int n;
    double a[N][N], b[N];
    bool solve() {
        // rep(i, 0, n - 1) {
        //     rep(j, 0, n - 1) { printf("%lf ", a[i][j]); }
        //     printf("| %lf\n", b[i]);
        // }
        rep(i, 0, n - 1) {
            if (a[i][i] == 0) {
                int k = i + 1;
                while (k < n && a[k][i] == 0) k++;
                if (k == n) return false;
                rep(j, i, n - 1) swap(a[i][j], a[k][j]);
                swap(b[i], b[k]);
            }
            rep(j, i + 1, n - 1) a[i][j] /= a[i][i];
            b[i] /= a[i][i];
            a[i][i] = 1;
            rep(k, 0, n - 1) {
                if (k == i) continue;
                rep(j, i + 1, n - 1) a[k][j] -= a[i][j] * a[k][i];
                b[k] -= b[i] * a[k][i];
                a[k][i] = 0;
            }
        }
        // rep(i, 0, n - 1) {
        //     rep(j, 0, n - 1) { printf("%lf ", a[i][j]); }
        //     printf("| %lf\n", b[i]);
        // }
        rep(i, 0, n - 2) if (b[i] < 0) return false;

        return true;
    }
} s;

void work() {
    int n;
    int a[N][N];
    scanf("%d", &n);
    rep(i, 0, n - 1) {
        rep(j, 0, n - 1) {
            scanf("%d", &a[i][j]);
            if (i == j)
                assert(a[i][j] == 0);
            else if (i > j)
                assert(a[i][j] == a[j][i]);
        }
    }
    s.n = n + 1;
    double ans = 0;
    rep(mask, 0, (1 << n) - 1) {
        rep(i, 0, n - 1) {
            if ((mask >> i) & 1) {
                rep(j, 0, n) s.a[i][j] = (i == j);
                s.b[i] = 0;
            } else {
                rep(j, 0, n - 1) s.a[i][j] = a[i][j];
                s.a[i][n] = -1;
                s.b[i] = 0;
            }
        }
        rep(j, 0, n) s.a[n][j] = (j != n);
        s.b[n] = 1;
        if (s.solve()) {
            // printf("mask: %d\n", mask);
            // rep(i, 0, n) printf("%lf ", s.b[i]);
            double tmp = 0;
            rep(i, 0, n - 1) rep(j, i + 1, n - 1) tmp +=
                a[i][j] * s.b[i] * s.b[j];
            // printf("\nscore: %lf\n", tmp);
            if (tmp > ans) {
                ans = tmp;
            }
        }
    }
    printf("%lf\n", ans);
}

int main() {
    work();
    return 0;
}