#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#include <atcoder/all>
using namespace atcoder;


int main(){
  int N; cin >> N;
  vector<int> A(N), B(N), a(N), b(N);
  for(int i = 0; i < N; i++)cin >> A[i];
  for(int i = 0; i < N; i++)cin >> B[i];
  double ans = 0, div = 0;
  for(int i = 0; i < N; i++)a[i] = i;
  do{
    for(int i = 0; i < N; i++)b[i] = i;
    do{
      int ca = 0, cb = 0;
      for(int i = 0; i < N; i++){
        if(A[a[i]] > B[b[i]])ca++;
        if(A[a[i]] < B[b[i]])cb++;
      }
      if(ca > cb)ans++;
      div++;
    }while(next_permutation(b.begin(), b.end()));
  }while(next_permutation(a.begin(), a.end()));
  ans /= div;
  cout << fixed << setprecision(8) << ans << endl;
}