#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin >> N;
  vector<int> A(N), B(N);
  for (auto&& e : A) {
    cin >> e;
  }
  for (auto&& e : B) {
    cin >> e;
  }
  vector<int> X(N), Y(N);
  iota(X.begin(), X.end(), 0);
  iota(Y.begin(), Y.end(), 0);
  int c = 0, a = 0;
  do {
    do {
      c++;
      int b = 0;
      for (int i = 0; i < N; i++) {
        if (A[X[i]] > B[Y[i]]) b++;
      }
      if (b > N / 2) a++;
    } while (next_permutation(Y.begin(), Y.end()));
  } while (next_permutation(X.begin(), X.end()));
  cout << fixed << setprecision(10) << (double)a / c << '\n';
  return 0;
}