#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cassert>
#include<cstdio>
#include<cctype>
#include<vector>
#include<bitset>
#include<random>
#include<ctime>
#include<queue>
#include<cmath>
#include<list>
#include<map>
#include<set>
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define pll pair<long long,long long>
#define FF fflush(stdout)
#define inf 0x3f3f3f3f
#define endl "\n"
#define fi first
#define se second
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
//char buf[1<<20],*p1,*p2;
//#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<20,stdin),p1==p2)?EOF:*p1++)
inline int read()
{
    int s=0,f=1;
    char x=getchar();
    while(!isdigit(x))f=(x=='-'?-1:1),x=getchar();
    while(isdigit(x))s=s*10+x-'0',x=getchar();
    return s*f;
}
const int p=1e9+7;
//ll ksm(int a,int b){ll ans=1,bs=a;while(b){if(b&1)ans=ans*bs%p;bs=bs*bs%p;b>>=1;}return ans;}
mt19937 rd(time(0));
#define reaD read
int w[13][13];
int e[13];
double ee[13];
int n;
double cal()
{
    int s=0;
    for(int i=1;i<=n;i++)
    s+=e[i];
    for(int i=1;i<=n;i++)
    ee[i]=1.0*e[i]/s;
    double ans=0;
    for(int i=1;i<=n;i++)
    for(int j=i+1;j<=n;j++)
    ans+=w[i][j]*ee[i]*ee[j];
    return ans;
}
double SA()
{
    double t=1000;
    double dt=0.997;
    double ans=0;
    while(t>1e-5)
    {
        int x=rd()%n+1;
        int del=(rd()%2?-1:1)*(rd()%100000);
        e[x]+=del;
        double tmp=cal();
        if(tmp>ans)
        {
            ans=tmp;
        }
        else if(exp((tmp-ans)/t)*RAND_MAX<=rand())
        {
            e[x]-=del;
        }
        if(t>1)t*=0.8;
        else
        t*=dt;
    }
    return ans;
}
int main()
{
    n=read();
    for(int i=1;i<=n;i++)
    for(int j=1;j<=n;j++)
    w[i][j]=read();
    for(int i=1;i<=n;i++)
    e[i]=rd()%100000;
    double ans=0;
    for(int i=1;i<=3000;i++)
    {
        ans=max(ans,SA());
    }
    printf("%.8lf",ans);
    //system("pause");
    return 0;
}