#include <bits/stdc++.h>
using namespace std;
template <class T>
T abs(T a) {
  return a >= 0 ? a : -a;
}
template <class T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <class T>
T mod(T a, T b) {
  T ret = a % b;
  if (ret < 0) ret += b;
  return ret;
}
long long mulmod(long long a, long long b, long long c) {
  if (b == 0LL) return 0LL;
  long long ret = mulmod(a, b >> 1, c);
  ret = (ret + ret) % c;
  if (b & 1LL) ret = (ret + a) % c;
  return ret;
}
long long powmod(long long a, long long b, long long c) {
  if (b == 0LL) return 1LL;
  long long ret = powmod(a, b >> 1, c);
  ret = ret * ret % c;
  if (b & 1LL) ret = ret * a % c;
  return ret;
}
template <class T>
inline void write(T x) {
  if (x < 0) putchar('-'), x = -x;
  if (x < 10)
    putchar(x + '0');
  else
    write(x / 10), putchar(x % 10 + '0');
}
template <class T>
inline void read(T& x) {
  bool f = 0;
  char ch;
  for (ch = getchar(); ch <= 32; ch = getchar())
    ;
  if (ch == '-') f = 1, ch = getchar();
  for (x = 0; ch > 32; ch = getchar()) x = (x << 3) + (x << 1) + ch - '0';
  if (f) x = -x;
}
double p[18][18], dp[1 << 18][18];
int main() {
  int n;
  read(n);
  for (register int i = 1; i <= n; ++i)
    for (register int j = 1; j <= n; ++j) scanf("%lf", &p[i - 1][j - 1]);
  dp[1][0] = 1.0;
  for (register int i = 0; i <= (1 << n) - 1; ++i)
    for (register int j = 0; j <= n - 1; ++j)
      if (i & (1 << j))
        for (register int k = 0; k <= n - 1; ++k)
          if (i & (1 << k))
            dp[i][j] = max(dp[i][j], p[j][k] * dp[i ^ (1 << k)][j] +
                                         p[k][j] * dp[i ^ (1 << j)][k]);
  double ans = 0.0;
  for (register int i = 0; i <= n - 1; ++i) ans = max(ans, dp[(1 << n) - 1][i]);
  return printf("%.12f\n", ans), 0;
}
