#include <bits/stdc++.h>
#define ms(x, v) memset(x, v, sizeof(x))
#define il __attribute__((always_inline)) static
#define U(i,l,r) for(int i(l),END##i(r);i<=END##i;++i)
#define D(i,r,l) for(int i(r),END##i(l);i>=END##i;--i)
using namespace std;
using ll = long long;

#define IC isdigit(c)
#define GC c=getchar()
void rd(auto &x) { x = 0; char GC; bool f = 0;
	for (; !IC; GC) f |= c == '-';
	for (; IC; GC) x = x * 10 + c - 48;
	if (f) x = -x;
}
void rd(auto &x, auto &...y) { rd(x); rd(y...); }
#define meow(...) fprintf(stderr, __VA_ARGS__)
#define Assert(e) if (!(e)) { meow("AF@%d\n", __LINE__); exit(__LINE__); }

const int N = 12;
int n, w[N][N], s;

double e[N][N] {}; int var[N] {};
void gen() {
	ms(e, 0);
	U (i, 1, n) if ((s >> i) & 1) {
		U (j, i + 1, n) if ((s >> j) & 1)
			e[i][j] = w[i][j];
		U (j, 1, i) if ((s >> j) & 1)
			e[i][j] = w[j][i];
		if (s & 1)
			e[i][n + 1] = 1;
	}
	if (s & 1) {
		U (i, 1, n) if ((s >> i) & 1)
			e[n + 1][i] = 1;
		e[n + 1][n + 2] = 1;
	}
}
const double EPS = 1e-9;
bool equ(double x, double y) { return abs(x - y) < EPS; }
int gauss() {
	int rk = 0; ms(var, 0);
	U (i, 1, n + 1) {
		int j = rk + 1; for (; j <= n + 1 && equ(e[j][i], 0); ++j);
		if (j > n + 1) continue;
		++rk; var[rk] = i;
		U (k, 1, n + 2) swap(e[rk][k], e[j][k]);
		for (j = 1; j <= n + 1; ++j) if (j != rk) {
			double c = e[j][i] / e[rk][i];
			U (k, 1, n + 2)
				e[j][k] -= e[rk][k] * c;
		}
	}
	return rk;
}

int main() {

	rd(n);
	U (i, 1, n) U (j, 1, n) rd(w[i][j]);
	double ans = -1;
	for (s = 0; s < (1 << (n + 1)); ++s) {
		gen();
		int rk = gauss();
		if (rk != __builtin_popcount(s))
			continue;
		double res[N] {}, cur = 0;
		U (i, 1, n + 1) if (var[i]) {
			if (equ(e[i][var[i]], 0) && !equ(e[i][n + 2], 0))
				goto CONT;
			if (var[i] <= n) {
				res[var[i]] = e[i][n + 2] / e[i][var[i]];
				if (res[var[i]] < 0)
					goto CONT;
			}
		}
		U (i, 1, n) U (j, i + 1, n)
			cur += res[i] * res[j] * w[i][j];
		ans = max(ans, cur);
CONT:;
	}
	printf("%.6lf\n", ans);
}