#include <iostream>
#include <algorithm>
#include <functional>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <ctime>
#include <cassert>
#include <complex>
#include <string>
#include <cstring>
#include <chrono>
#include <random>
#include <bitset>
#include <array>
#include<utility>
#include<stack>
#include <iomanip>
using namespace std;
#define int long long
#define P pair<int,int>
#define Graph vector<vector<int>>
#define float long double
#define rep(i,a,b) for(int i=(a);i<(b);++i)
#define repi(itr,m) for(auto itr=(m).begin();itr!=(m).end();itr++)
#define all(a) (a).begin(), (a).end()
#define vi vector<int>
const int INF=100000000000000;
vector<int>dx4={-1,1,0,0};
vector<int>dy4={0,0,-1,1};
vector<int>dx8={-1,-1,-1,0,0,1,1,1};
vector<int>dy8={-1,0,1,-1,1,-1,0,1};
template<typename T> inline bool chmax(T &a, T b) { return ((a < b) ? (a = b, true) : (false));}
template<typename T> inline bool chmin(T &a, T b) { return ((a > b) ? (a = b, true) : (false));}

int solve(){
  int n;
  cin>>n;
  float ans=0;
  float cnt=0;
  vector<int>a(n);
  vector<int>b(n);
  rep(i,0,n){cin>>a[i];}
  rep(i,0,n){cin>>b[i];}
  sort(all(a));
  sort(all(b));
  do {
    do {
      int num=0;
      cnt++;
      rep(i,0,n){
        if(a[i]>b[i]){
          num++;
        }
      }
      if(num*2>n){
        ans++;
      }
    } while (next_permutation(all(b)));
  } while (next_permutation(all(a)));
  cout<<fixed<<setprecision(10)<<(ans/cnt)<<endl;
  return 0;
}

signed main(){
  solve();
}