#include<bits/stdc++.h>
#define L(i, j, k) for(int i = (j); i <= (k); ++i)
#define R(i, j, k) for(int i = (j); i >= (k); --i)
#define ll long long
#define vi vector <int>
#define sz(a) ((int) (a).size())
#define me(f, x) memset(f, x, sizeof(f))
#define uint unsig7ned int
#define ull unsigned long long 
#define i128 __int128
using namespace std;
const int N = 17;
int n;

double a[N][N];
double f[N];
inline double calc() {
	double sum = 0, bt = 0;
	L(i, 1, n) {
		bt += f[i];
	}
	L(i, 1, n) {
		L(j, i + 1, n) {
			sum += f[i] * f[j] * a[i][j];
		}
	}
	if(fabs(bt) < 1e-9) 
		return 0;
	return sum / bt / bt;
}

mt19937_64 orz;
double Get() {
	ll d = 1LL << 40;
	ll x = orz() % (d * 2 + 1) - d;
	return (double)x / d; 
}
int main() {
	ios :: sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	cin >> n;
	L(i, 1, n) {
		L(j, 1, n) {
			cin >> a[i][j];
		}
	}
//	n = 10;
//	L(i, 1, n) {
//		L(j, 1, n) {
//			a[i][j] = orz() % 1000 + 1;
//		}
//	}
	double ans = 0;
	L(o, 1, 10) {
		L(i, 1, n) 
			f[i] = fabs(Get());
		if(o <= 5) {
		double cur = Get();
		for(double temp = 100; temp > 1e-9; temp *= 0.999) {
			int pos = orz() % n + 1;
			double lst = f[pos];
			f[pos] += Get() * temp, f[pos] = max(f[pos], 0.);
			double nw = calc();
			if(nw > cur) {
				cur = nw;
			} else {
				f[pos] = lst;
			}
		}
		ans = max(ans, calc());	
		} else {
		double cur = Get();
		for(double temp = 100; temp > 1e-9; temp *= 0.999) {
			int pos = orz() % n + 1;
			double lst = f[pos];
			f[pos] += Get() * temp, f[pos] = max(f[pos], 0.);
			double nw = calc();
			if(nw > cur || exp(nw - cur) > 10 * (Get() + 1)) {
				cur = nw;
			} else {
				f[pos] = lst;
			}
		}
		ans = max(ans, calc());
		}
		
	}
	cout.precision(12); cout << fixed; 
	cout << ans << '\n';
	return 0;
}