/* -*- coding: utf-8 -*-
 *
 * 133.cc: No.133 カードゲーム - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 4;

/* typedef */

/* global variables */

int as[MAX_N], bs[MAX_N], ps[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  cin >> n;

  for (int i = 0; i < n; i++) cin >> as[i];
  for (int i = 0; i < n; i++) cin >> bs[i];
  for (int i = 0; i < n; i++) ps[i] = i;

  int cnt = 0;
  do {
    int aw = 0, bw = 0;
    for (int i = 0; i < n; i++) {
      if (as[i] > bs[ps[i]]) aw++;
      else if (as[i] < bs[ps[i]]) bw++;
    }
    if (aw > bw) cnt++;
  } while (next_permutation(ps, ps + n));

  int fn = 1;
  for (int i = 1; i <= n; i++) fn *= i;

  printf("%.6lf\n", (double)cnt / fn);
  return 0;
}