#include<bits/stdc++.h>
using namespace std;

double res[15];
double w[15][15];
double sum;
int n;

void calc(){
    sum=0;
    for(int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++)
            sum+=res[i]*res[j]*w[i][j];  
}

int main(){
    res[1]=1;
    cin>>n;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++)
            cin>>w[i][j];
    double T = 1;
    double delta = 0.999;
    while(T>=1e-6){
        int x = rand() % n + 1, y = rand() % n + 1;
        double nres = sum;
        double d = min({T,res[x]});
        res[x] -= d;
        res[y] += d;
        calc();
        if(sum<nres)res[x]+=d,res[y]-=d;
        T *= delta;
    }
    calc();
    cout << sum << endl;
}