#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;

  vector<int> a(n), b(n);

  REP (i, n) cin >> a[i];
  REP (i, n) cin >> b[i];

  sort(b.begin(), b.end());

  int w = 0;
  int t = 0;
  
  do {
    ++t;
    int c = 0;
    REP (i, n) c += a[i] > b[i];
    if (2 * c > n)
      ++w;
  } while (next_permutation(b.begin(), b.end()));

  double ret = 1.0 * w / t;
  cout << fixed << setprecision(12) << ret << endl;
  
  return 0;
}