#include<bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < n; i++)
#define pb push_back
using namespace std;
typedef long long ll;

int main(){
  int n;
  cin>>n;
  vector<int> a(n),b(n);
  rep(i,n) cin>>a[i];
  rep(i,n) cin>>b[i];
  int res = 0;
  
  sort(a.begin(),a.end());
  sort(b.begin(),b.end());
  
  do{
    do{
      int win = 0;
      rep(i,n) if(a[i]>b[i]) win++;
      if(win > n/2) res++;
    }while(next_permutation(b.begin(),b.end()));
  }while(next_permutation(a.begin(),a.end()));
  
  double ans = (double)res; 
  rep(i,n) ans /= (i+1)*(i+1);
  printf("%f\n",ans);
}