#include <bits/stdc++.h>
using namespace std;
template <typename T>
T in() {
  char ch;
  T n = 0;
  bool ng = false;
  while (1) {
    ch = getchar();
    if (ch == '-') {
      ng = true;
      ch = getchar();
      break;
    }
    if (ch >= '0' && ch <= '9') break;
  }
  while (1) {
    n = n * 10 + (ch - '0');
    ch = getchar();
    if (ch < '0' || ch > '9') break;
  }
  return (ng ? -n : n);
}
template <typename T>
inline T POW(T B, T P) {
  if (P == 0) return 1;
  if (P & 1)
    return B * POW(B, P - 1);
  else
    return (POW(B, P / 2) * POW(B, P / 2));
}
template <typename T>
inline T Gcd(T a, T b) {
  if (a < 0) return Gcd(-a, b);
  if (b < 0) return Gcd(a, -b);
  return (b == 0) ? a : Gcd(b, a % b);
}
template <typename T>
inline T Lcm(T a, T b) {
  if (a < 0) return Lcm(-a, b);
  if (b < 0) return Lcm(a, -b);
  return a * (b / Gcd(a, b));
}
long long Bigmod(long long base, long long power, long long MOD) {
  long long ret = 1;
  while (power) {
    if (power & 1) ret = (ret * base) % MOD;
    base = (base * base) % MOD;
    power >>= 1;
  }
  return ret;
}
bool isVowel(char ch) {
  ch = toupper(ch);
  if (ch == 'A' || ch == 'U' || ch == 'I' || ch == 'O' || ch == 'E')
    return true;
  return false;
}
template <typename T>
long long int isLeft(T a, T b, T c) {
  return (a.x - b.x) * (b.y - c.y) - (b.x - c.x) * (a.y - b.y);
}
long long ModInverse(long long number, long long MOD) {
  return Bigmod(number, MOD - 2, MOD);
}
bool isConst(char ch) {
  if (isalpha(ch) && !isVowel(ch)) return true;
  return false;
}
int toInt(string s) {
  int sm;
  stringstream second(s);
  second >> sm;
  return sm;
}
int n;
double a[19][19];
double dp[19][(1 << 18) + 10];
int vs[19][(1 << 18) + 10];
int lm;
double Solve(int w, int m) {
  if (m == lm) {
    if (w == 0) return 1.0;
    return 0.0;
  }
  double &res = dp[w][m];
  if (vs[w][m]) return res;
  vs[w][m] = 1;
  res = 0.0;
  for (int i = 0; i < n; i++) {
    if ((m & (1 << i)) == 0) {
      double aa = a[w][i] * Solve(w, (m | (1 << i)));
      aa += a[i][w] * Solve(i, (m | (1 << i)));
      res = max(res, aa);
    }
  }
  return res;
}
int main() {
  cin >> n;
  lm = (1 << n) - 1;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++) cin >> a[i][j];
  if (n == 1) {
    printf("1.00\n");
    return 0;
  } else if (n == 2) {
    printf("%.10lf\n", a[0][1]);
    return 0;
  }
  double ans = 0.0;
  for (int j = 0; j < n; j++) {
    for (int i = j + 1; i < n; i++) {
      double aa = a[j][i] * Solve(j, (1 << j) | (1 << i));
      aa += a[i][j] * Solve(i, (1 << i) | (1 << j));
      ans = max(aa, ans);
    }
  }
  printf("%.10lf\n", ans);
  return 0;
}
