#include<bits/stdc++.h>
#define eps 1e-8
using namespace std;
int w[15][15];
int aa[15];
double a[15][15];
double qz[15];
int main(){
	int n;
	scanf("%d",&n);
	for(int i=1;i<=n;++i)for(int j=1;j<=n;++j)
		scanf("%d",&w[i][j]);
	double ans=0;
	for(int S=0;S<(1<<n)-1;++S){
		int m=0;
		for(int i=1;i<=n;++i)if(!((S>>(i-1))&1))aa[++m]=i;
		for(int i=1;i<=m;++i){
			for(int j=1;j<=m;++j)a[i][j]=w[aa[i]][aa[j]];
			a[i][m+1]=-1;a[i][m+2]=0;
		}
		for(int i=1;i<=m;++i)a[m+1][i]=1;
		a[m+1][m+1]=0;a[m+1][m+2]=1;
		int fl=1;
		for(int i=1;i<=m+1;++i){
			if(fabs(a[i][i])<eps){
				for(int j=i+1;j<=m+1;++j)if(fabs(a[j][i])>eps){
					for(int k=1;k<=m+2;++k)swap(a[i][k],a[j][k]);
					break;
				}
			}
			if(fabs(a[i][i])<eps){
				fl=0;
				break;
			}
			for(int j=i+1;j<=m+1;++j){
				double cj=-a[j][i]/a[i][i];
				for(int k=i;k<=m+2;++k)a[j][k]+=a[i][k]*cj;
			}
		}
		if(!fl)continue;
		for(int i=m+1;i>=1;--i){
			qz[i]=a[i][m+2];
			for(int j=i+1;j<=m+1;++j)qz[i]-=qz[j]*a[i][j];
			qz[i]/=a[i][i];
			if(i<=m)fl&=(qz[i]>0);
		}
		if(!fl)continue;
		double he=0;
		for(int i=1;i<=m;++i)for(int j=i+1;j<=m;++j)
			he+=qz[i]*qz[j]*w[aa[i]][aa[j]];
		ans=max(ans,he);
	}
	printf("%.6f\n",ans);
	return 0;
}