/*FreeTimeLove's code.
Love has a nasty habit of disappearing over night.*/
#include<bits/stdc++.h>
namespace FRTMLV{
#define ll long long
#define LD long double
#define i7 __int128
#define re return
#define con continue
using namespace std;
template<class T>inline bool ckmin(T &a,T b){re b<a?a=b,1:0;}
template<class T>inline bool ckmax(T &a,T b){re a<b?a=b,1:0;}
const int N=1e5+5;
inline int rd(){
	int ans=0,f=0;
	char ch=getchar();
	while(ch<'0'||ch>'9')f^=(ch=='-'),ch=getchar();
	while(ch>='0'&&ch<='9')ans=(ans<<3)+(ans<<1)+(ch^48),ch=getchar();
	re f?-ans:ans;
}
int n,w[11][11];
LD e[11],eps=1e-15;
mt19937 rnd(chrono::system_clock::now().time_since_epoch().count());
LD calc(){
	LD ans=0;
	for(int i=1;i<=n;i++)
		for(int j=i+1;j<=n;j++)ans+=e[i]*e[j]*w[i][j];
	re ans;
}
int main(){
	n=rd();
	ll Sum=0;
	for(int i=1;i<=n;i++)
		for(int j=1;j<=n;j++)w[i][j]=rd(),Sum+=w[i][j];
	if(!Sum){
		puts("0");re 0;
	}
	LD mxans=0;
	for(int T=1;T<=1;T++){
		for(int i=1;i<=n;i++)e[i]=1.0/n;
		LD ans=calc();
		for(int i=1;i<=5000000;i++){
			int u=rnd()%n+1,v=rnd()%n+1;
			while(u==v)v=rnd()%n+1;
			LD W1=0,W2=0,k=e[u]+e[v];
			for(int j=1;j<=n;j++)
				if(j!=u&&j!=v)W1+=e[j]*w[u][j],W2+=e[j]*w[v][j];
			LD nk=(k*w[u][v]+W1-W2)/2/w[u][v];
			if(nk<0)nk=0;
			if(nk>k)nk=k;
			e[u]=nk,e[v]=k-nk;
			LD newnew=calc();
			if(ans>newnew+eps){
				puts("Fuck");
			}
			ckmax(ans,newnew);
		}
		ckmax(mxans,ans);
	}
	printf("%.15Lf\n",mxans);
	re 0;
}
/*
2
0 1
1 0
*/
}int main(){re FRTMLV::main();}