#include <bits/stdc++.h>

using namespace std;

template<typename T> inline T gcd(T a, T b) {
  return __gcd(a, b);
}

template<typename T> inline T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}

template<typename T> inline T floor(T a, T b) {
  return a / b * b <= a ? a / b : a / b - 1;
}

template<typename T> inline T ceil(T a, T b) {
  return floor(a + b - 1, b);
}

template<typename T> inline T round(T a, T b) {
  return floor(a + b / 2);
}

template<typename T> inline T mod(T a, T b) {
  return a - floor(a, b) * b;
}

template<typename T> inline T factorial(T n) {
  return n <= 1 ? 1 : factorial(n - 1) * n;
}

int main() {
  int n;
  cin >> n;
  vector<int> a(n), b(n);
  for (int& i : a) cin >> i;
  for (int& i : b) cin >> i;
  sort(a.begin(), a.end());
  sort(b.begin(), b.end());
  int c = 0;
  do {
    do {
      int r = 0;
      for (int i = 0; i < n; ++i) {
        if (a[i] > b[i]) ++r;
        if (a[i] < b[i]) --r;
      }
      if (r > 0) ++c;
    } while (next_permutation(b.begin(), b.end()));
  } while (next_permutation(a.begin(), a.end()));
  cout << fixed << setprecision(15) << c / pow(factorial(n), 2);
}