#include <bits/stdc++.h>

using namespace std;

int mark[16];

double p[16][16];

vector <int> ord;

int main(){

cin.tie(0);

ios_base::sync_with_stdio(0);

int n;

double ans = 0.0, prod = 1.0;

cin >> n;

for(int i = 0; i < n; ++i)

for(int j = 0; j < n; ++j)

cin >> p[i][j];

for(int i = 0; i < n; ++i) ord.push_back(i);

while(1){

prod = 1.0;

memset(mark, 0, sizeof mark);

for(int i = 0; i < n; ++i){

mark[ord[i]] = 1;

for(int j = 0; j < n; ++j)

if(!mark[j]) prod *= p[ord[i]][j];

}

ans += prod;

if(!next_permutation(ord.begin(), ord.end())) break;

}

cout << fixed << setprecision(15) << ans << "\n";

return 0;

}