#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
using pii = pair<int, int>;

int fact(int n) {
  if (n == 0) {
    return 1;
  } else {
    return n * fact(n - 1);
  }
}
int main() {
  int n;
  cin >> n;
  vector<int> a(n), b(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  for (int i = 0; i < n; i++) {
    cin >> b[i];
  }
  sort(a.begin(), a.end());
  sort(b.begin(), b.end());
  int ans = 0;
  do {
    do {
      int win = 0;
      for (int i = 0; i < n; i++) {
        if (a[i] > b[i]) {
          win++;
        }
      }
      if (win > n - win) ans++;

    } while (next_permutation(b.begin(), b.end()));
  } while (next_permutation(a.begin(), a.end()));

  // cout << ans << endl;
  printf("%.7lf\n", (double)ans / (fact(n) * fact(n)));
}