// copied from https://judge.yosupo.jp/submission/109508

#line 1 "main.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/system_of_linear_equations"
#line 1 "library/my_template.hpp"
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")

#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using pi = pair<ll, ll>;
using vi = vector<ll>;
using u32 = unsigned int;
using u64 = unsigned long long;
using i128 = __int128;

template <class T>
using vc = vector<T>;
template <class T>
using vvc = vector<vc<T>>;
template <class T>
using vvvc = vector<vvc<T>>;
template <class T>
using vvvvc = vector<vvvc<T>>;
template <class T>
using vvvvvc = vector<vvvvc<T>>;
template <class T>
using pq = priority_queue<T>;
template <class T>
using pqg = priority_queue<T, vector<T>, greater<T>>;

#define vec(type, name, ...) vector<type> name(__VA_ARGS__)
#define vv(type, name, h, ...) \
  vector<vector<type>> name(h, vector<type>(__VA_ARGS__))
#define vvv(type, name, h, w, ...)   \
  vector<vector<vector<type>>> name( \
      h, vector<vector<type>>(w, vector<type>(__VA_ARGS__)))
#define vvvv(type, name, a, b, c, ...)       \
  vector<vector<vector<vector<type>>>> name( \
      a, vector<vector<vector<type>>>(       \
             b, vector<vector<type>>(c, vector<type>(__VA_ARGS__))))

// https://trap.jp/post/1224/
#define FOR1(a) for (ll _ = 0; _ < ll(a); ++_)
#define FOR2(i, a) for (ll i = 0; i < ll(a); ++i)
#define FOR3(i, a, b) for (ll i = a; i < ll(b); ++i)
#define FOR4(i, a, b, c) for (ll i = a; i < ll(b); i += (c))
#define FOR1_R(a) for (ll i = (a)-1; i >= ll(0); --i)
#define FOR2_R(i, a) for (ll i = (a)-1; i >= ll(0); --i)
#define FOR3_R(i, a, b) for (ll i = (b)-1; i >= ll(a); --i)
#define FOR4_R(i, a, b, c) for (ll i = (b)-1; i >= ll(a); i -= (c))
#define overload4(a, b, c, d, e, ...) e
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FOR_R(...) \
  overload4(__VA_ARGS__, FOR4_R, FOR3_R, FOR2_R, FOR1_R)(__VA_ARGS__)

#define FOR_subset(t, s) for (ll t = s; t >= 0; t = (t == 0 ? -1 : (t - 1) & s))
#define all(x) x.begin(), x.end()
#define len(x) ll(x.size())
#define elif else if

#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second

#define stoi stoll

template <typename T, typename U>
T SUM(const vector<U> &A) {
  T sum = 0;
  for (auto &&a: A) sum += a;
  return sum;
}

#define MIN(v) *min_element(all(v))
#define MAX(v) *max_element(all(v))
#define LB(c, x) distance((c).begin(), lower_bound(all(c), (x)))
#define UB(c, x) distance((c).begin(), upper_bound(all(c), (x)))
#define UNIQUE(x) sort(all(x)), x.erase(unique(all(x)), x.end())

int popcnt(int x) { return __builtin_popcount(x); }
int popcnt(u32 x) { return __builtin_popcount(x); }
int popcnt(ll x) { return __builtin_popcountll(x); }
int popcnt(u64 x) { return __builtin_popcountll(x); }
// (0, 1, 2, 3, 4) -> (-1, 0, 1, 1, 2)
int topbit(int x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); }
int topbit(u32 x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); }
int topbit(ll x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); }
int topbit(u64 x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); }
// (0, 1, 2, 3, 4) -> (-1, 0, 1, 0, 2)
int lowbit(int x) { return (x == 0 ? -1 : __builtin_ctz(x)); }
int lowbit(u32 x) { return (x == 0 ? -1 : __builtin_ctz(x)); }
int lowbit(ll x) { return (x == 0 ? -1 : __builtin_ctzll(x)); }
int lowbit(u64 x) { return (x == 0 ? -1 : __builtin_ctzll(x)); }

template <typename T>
T pick(deque<T> &que) {
  T a = que.front();
  que.pop_front();
  return a;
}

template <typename T>
T pick(pq<T> &que) {
  T a = que.top();
  que.pop();
  return a;
}

template <typename T>
T pick(pqg<T> &que) {
  assert(que.size());
  T a = que.top();
  que.pop();
  return a;
}

template <typename T>
T pick(vc<T> &que) {
  assert(que.size());
  T a = que.back();
  que.pop_back();
  return a;
}

template <typename T, typename U>
T ceil(T x, U y) {
  return (x > 0 ? (x + y - 1) / y : x / y);
}

template <typename T, typename U>
T floor(T x, U y) {
  return (x > 0 ? x / y : (x - y + 1) / y);
}

template <typename T, typename U>
pair<T, T> divmod(T x, U y) {
  T q = floor(x, y);
  return {q, x - q * y};
}

template <typename F>
ll binary_search(F check, ll ok, ll ng) {
  assert(check(ok));
  while (abs(ok - ng) > 1) {
    auto x = (ng + ok) / 2;
    tie(ok, ng) = (check(x) ? mp(x, ng) : mp(ok, x));
  }
  return ok;
}

template <typename F>
double binary_search_real(F check, double ok, double ng, int iter = 100) {
  FOR(iter) {
    double x = (ok + ng) / 2;
    tie(ok, ng) = (check(x) ? mp(x, ng) : mp(ok, x));
  }
  return (ok + ng) / 2;
}

template <class T, class S>
inline bool chmax(T &a, const S &b) {
  return (a < b ? a = b, 1 : 0);
}
template <class T, class S>
inline bool chmin(T &a, const S &b) {
  return (a > b ? a = b, 1 : 0);
}

vc<int> s_to_vi(const string &S, char first_char) {
  vc<int> A(S.size());
  FOR(i, S.size()) { A[i] = S[i] - first_char; }
  return A;
}

template <typename T, typename U>
vector<T> cumsum(vector<U> &A, int off = 1) {
  int N = A.size();
  vector<T> B(N + 1);
  FOR(i, N) { B[i + 1] = B[i] + A[i]; }
  if (off == 0) B.erase(B.begin());
  return B;
}

template <typename CNT, typename T>
vc<CNT> bincount(const vc<T> &A, int size) {
  vc<CNT> C(size);
  for (auto &&x: A) { ++C[x]; }
  return C;
}

// stable
template <typename T>
vector<int> argsort(const vector<T> &A) {
  vector<int> ids(A.size());
  iota(all(ids), 0);
  sort(all(ids),
       [&](int i, int j) { return A[i] < A[j] || (A[i] == A[j] && i < j); });
  return ids;
}

// A[I[0]], A[I[1]], ...
template <typename T>
vc<T> rearrange(const vc<T> &A, const vc<int> &I) {
  int n = len(I);
  vc<T> B(n);
  FOR(i, n) B[i] = A[I[i]];
  return B;
}
#line 1 "library/other/io.hpp"
// based on yosupo's fastio
#include <unistd.h>

namespace detail {
template <typename T, decltype(&T::is_modint) = &T::is_modint>
std::true_type check_value(int);
template <typename T>
std::false_type check_value(long);
} // namespace detail

template <typename T>
struct is_modint : decltype(detail::check_value<T>(0)) {};
template <typename T>
using is_modint_t = enable_if_t<is_modint<T>::value>;
template <typename T>
using is_not_modint_t = enable_if_t<!is_modint<T>::value>;

/*
0 行目に解のひとつ。
1～行目に解空間の基底が行ベクトルとして入る。
解なし = empty
*/
long double eps=1e-12;
template <typename T>
vc<vc<T>> solve_linear(vc<vc<T>> a, vc<T> b) {
  auto n = len(a), m = len(a[0]);
  int rk = 0;
  FOR(j, m) {
    if (abs(a[rk][j]) < eps)
    {
      FOR3(i, rk + 1, n) if (abs(a[i][j]) > eps) {
        swap(a[rk], a[i]);
        swap(b[rk], b[i]);
        break;
      }
    }
    if (abs(a[rk][j]) < eps) continue;
    T c = T(1) / a[rk][j];
    for (auto&& x: a[rk]) x *= c;
    b[rk] *= c;
    FOR(i, n) if (i != rk) {
      T c = a[i][j];
      b[i] -= b[rk] * c;
      FOR3(k, j, m) { a[i][k] -= a[rk][k] * c; }
    }
    ++rk;
    if (rk == n) break;
  }
  //  cerr<<"rk="<<rk<<","<<"n="<<n<<endl;
  FOR3(i, rk, n) if (abs(b[i]) > 0) return {};
  vc<vc<T>> res(1, vc<T>(m));
  vc<int> pivot(m, -1);
  int p = 0;
  FOR(i, rk) {
    while (abs(a[i][p]) < eps) ++p;
    res[0][p] = b[i];
    pivot[p] = i;
  }
  FOR(j, m) if (pivot[j] == -1) {
    vc<T> x(m);
    x[j] = -1;
    FOR(k, j) if (pivot[k] != -1) x[k] = a[pivot[k]][j];
    res.eb(x);
  }
  return res;
}

int m;
int c[10][10];
long double solve(){
    /*cerr<<"=========="<<endl;
    cerr<<"m="<<m<<endl;
    for(int i=0;i<m;i++){
        for(int j=0;j<m;j++)cerr<<c[i][j]<<" "; cerr<<endl;
    }*/
    vector<vector<long double>> A;
    vector<long double> b(m,0.); b[0]=1.;
    A.push_back(vector<long double>(m,1.));
    for(int i=0;i+1<m;i++){
        A.push_back(vector<long double>(m));
        for(int j=0;j<m;j++){
            A[i+1][j]=c[i][j]-c[i+1][j];
        }
    }
    /*cerr<<"A"<<endl;
    for(int i=0;i<m;i++){
        for(int j=0;j<m;j++)cerr<<A[i][j]<<" "; cerr<<endl;
    }
    cerr<<"b"<<endl;
    for(int j=0;j<m;j++)cerr<<b[j]<<" "; cerr<<endl;*/
    auto res=solve_linear(A,b);
    //cerr<<"res.size()="<<res.size()<<endl;
    //if(res.size()==0)cerr<<0.<<endl;
    if(res.size()==0)return 0;
    for(int i=0;i<m;i++)if(res[0][i]<eps)return 0.;
    auto ret=0.;
    for(int i=0;i<m;i++)for(int j=i+1;j<m;j++){
        ret+=c[i][j]*res[0][i]*res[0][j];
    }
    //cerr<<ret<<endl;
    return ret;
}

signed main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.precision(20);
    
    int n;
    int a[10][10];
    cin>>n;
    for(int i=0;i<n;i++)for(int j=0;j<n;j++)cin>>a[i][j];
    for(int i=0;i<n;i++){
        a[i][i]=0;
        for(int j=0;j<i;j++){
            a[i][j]=a[j][i];
        }
    }
    
    long double ret=0.;
    for(int i=1;i<(1<<n);i++){
        vector<int> v;
        for(int j=0;j<n;j++){
            if((i>>j)&1){
                v.push_back(j);
            }
        }
        m=v.size();
        for(int j=0;j<v.size();j++)for(int k=0;k<v.size();k++){
            c[j][k]=a[v[j]][v[k]];
        }
        ret=max(ret,solve());
    }
    cout<<ret<<endl;
}