#include<bits/stdc++.h>
using namespace std;
#define il inline
#define fi first
#define se second
#define mk make_pair
#define eb emplace_back
#define rep(i,l,r) for(int i=(l); i<=(r); ++i)
#define rep_(i,l,r) for(int i=(l); i>=(r); --i)
typedef long long lr;
typedef double db;
typedef pair<int,int> pii;
typedef vector<int> vi;
constexpr int mod1=998244353,mod2=1e9+7;
constexpr db pi=3.141592653589793,eps=1e-9;
constexpr int inf32=0x3f3f3f3f,Inf32=0xc0c0c0c0;
constexpr lr inf64=0x3f3f3f3f3f3f3f3f,Inf64=0xc0c0c0c0c0c0c0c0;
template<typename T>il T Max(T x,T y) { return (x>y)? x:y; }
template<typename T>il T Min(T x,T y) { return (x<y)? x:y; }
template<typename T>il T gcd(T x,T y) { return (!y)? x:gcd(y,x%y); }
template<typename T>il T Abs(T x) { return (x>0)? x:(-x); }
template<typename T>il T Rnd(T l,T r,mt19937_64 &eng)
{
	uniform_int_distribution<T> uid(l,r);
	return uid(eng);
}
mt19937_64 eng(chrono::high_resolution_clock::now().time_since_epoch().count());
constexpr int N=15;
int n,val[N],w[N][N];
db p[N];
il void chk(int x,int y)
{
	db X=0,Y=0;
	rep(i,1,n)
		if(i!=x&&i!=y)
			X+=p[i]*w[x][i],Y+=p[i]*w[y][i];
	db xx=0.5*(X-Y+w[x][y]*(p[x]+p[y]))/w[x][y],yy=0.5*(Y-X+w[x][y]*(p[x]+p[y]))/w[x][y];
	p[x]=xx,p[y]=yy;
}
il void Solve()
{
	cin>>n;
	rep(i,1,n)
		rep(j,1,n)
			cin>>w[i][j];
	db bp=0;
	int Q=150;
	while(Q--)
	{
		int sum=0;
		rep(i,1,n)
			val[i]=Rnd(20210416,80000000,eng),sum+=val[i];
		rep(i,1,n)
			p[i]=1.0*val[i]/sum;
		rep(i,1,40000)
		{
			int x=Rnd(1,n,eng),y=Rnd(1,n,eng);
			while(x==y)
				x=Rnd(1,n,eng),y=Rnd(1,n,eng);
			chk(x,y);
		}
		db ans=0;
		rep(i,1,n)
			rep(j,i+1,n)
				ans+=p[i]*p[j]*w[i][j];
		bp=Max(bp,ans);
	}
	cout<<setiosflags(ios::fixed)<<setprecision(9)<<bp<<'\n';
}
int main()
{
#ifdef LOCAL
	string fpre="test",isuf="in",osuf="out";
	assert(freopen((fpre+"."+isuf).c_str(),"r",stdin));
	assert(freopen((fpre+"."+osuf).c_str(),"w",stdout));
#endif
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	int T=1;
	while(T--)
		Solve();
	return 0;
}