#include <bits/stdc++.h>
using namespace std;const double eps=1e-10;using ll=long long;const int M=998244353;
struct Mat{
	int n,m;vector<vector<double>>mat;vector<int>sol;Mat(int _n,int _m){ini(_n,_m);}
	void ini(int _n,int _m){n=_n,m=_m,mat.resize(n,vector<double>(m,0));}
	int Gauss(){//0:none/1:only sol/2:multi sol
		int pt=0;for(int c=0;c<n;c++){
			int t=pt;for(int i=pt;i<n;i++)if(abs(mat[i][c])>abs(mat[t][c]))t=i;
			if(abs(mat[t][c])<eps)continue;swap(mat[t],mat[pt]);for(int i=m-1;i>=c;i--)mat[pt][i]/=mat[pt][c];
			for(int i=0;i<n;i++)if(pt!=i&&abs(mat[i][c])>eps)for(int j=m-1;j>=c;j--)mat[i][j]-=mat[pt][j]*mat[i][c];pt++;}
		if(pt==n)return 1;for(int i=pt;i<n;i++)for(int j=n;j<m;j++)if(abs(mat[i][j])>eps)return 0;return 2;}
	void outp(){for(int i=0;i<n;i++)for(int j=0;j<m;j++)cout<<mat[i][j]<<" \n"[j==m-1];cout<<"%%%\n";}};
struct S
{
	int n;
	void solve()
	{
		cin>>n;vector<vector<int>>a(n,vector<int>(n));for(auto &k:a)for(auto&kk:k)cin>>kk;int B=(1<<n);double mx=0;
		for(int k=0;k<B;k++)
		{
			Mat A(n,n+1);for(int i=0;i<n;A.mat[i++][n]=1)if(k&(1<<i))
				for(int j=0;j<n;j++)if((k&(1<<i))&&i!=j)A.mat[i][j]=(i<j)?a[i][j]:a[j][i];
			//A.outp();
			A.Gauss();
			//A.outp();
			vector<double>res(n,0);double sum=0;
			for(int i=0;i<n;i++)for(int j=0;j<n;j++)if(abs(A.mat[i][j])>eps){res[j]=A.mat[i][n],sum+=res[j];break;}
			//for(auto k:res)cout<<k<<'_';cout<<'\n';
			if(abs(sum)<eps)continue;for(auto &k:res)k/=sum;sum=0;
			for(int i=0;i<n;i++)for(int j=i+1;j<n;j++)sum+=res[i]*res[j]*a[i][j];
			mx=max(mx,sum);//cout<<sum<<'\n';
		}	
		cout<<mx<<'\n';
	}
};
int main()
{
	//freopen("1.in","r",stdin);
	cout<<fixed<<setprecision(12);
	ios::sync_with_stdio(0);cin.tie(0);
	int t=1;/*cin>>t;*/
	while(t--){S SS;SS.solve();}
}