#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>

using namespace std;

int main(){
  int N; cin >> N;
  vector<int> index(N);
  for(int i = 0;i < N;i++)index[i] = i;

  vector<int> a(N);
  vector<int> b(N);
  for(int i = 0;i < N;i++)cin >> a[i];
  for(int i = 0;i < N;i++)cin >> b[i];

  int a_win = 0;
  int perm_num = 0;
  do{
    int win = 0;
    for(int i = 0;i < N;i++){
      if(a[index[i]] > b[i])win++;
    }

    if(win > N/2)a_win++;
    perm_num++;
  }while(next_permutation(index.begin(),index.end()));

  printf("%.10lf",(double)a_win/perm_num);

}