#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using T = tuple<int, int, int>;
#define al(a) a.begin(), a.end()
#define ral(a) a.rbegin(), a.rend()
#define sz(a) (int)a.size()
#define db(a, b) cout << #a << ": " << a << " " << #b << ": " << b << endl;

int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; ++i) { cin >> a[i]; }
  vector<int> b(n);
  for (int i = 0; i < n; ++i) { cin >> b[i]; }
  sort(al(a));
  sort(al(b));

  double ans = 0;
  int tot = 0;
  do {
    do {
      tot++;
      int cnt = 0;
      for (int i = 0; i < n; ++i) {
        if (a[i] > b[i]) cnt++;
      }
      if (cnt >= (n + 1) / 2) ans++;
    } while (next_permutation(al(b)));
  } while (next_permutation(al(a)));
//   db(ans, tot);
  ans = ans / tot;
  cout << fixed << setprecision(15) << ans << endl;
  return 0;
}