#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string>
#include<string.h>
#include<math.h>
#include<stdlib.h>
#include<vector>
#include<queue>
#include<map>
#define rep(index,num) for(int index=0;index<num;index++)
#define rep1(index,num) for(int index=1;index<=num;index++)
#define scan(argument) cin>>argument
#define prin(argument) cout<<argument<<endl
#define kaigyo cout<<endl
#define eps 1e-15
#define mp(a1,a2) make_pair(a1,a2)
typedef long long ll;
using namespace std;
typedef pair<ll,ll> pll;
typedef pair<int,int> pint;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef vector<pint> vpint;
typedef vector<pll> vpll;
ll INFl=1e+18+1;
int INF=1e+9+1;
int kaijo(int m){
	int ans=1;
	rep1(i,m){
		ans*=i;
	}
	return ans;
}
int main(){
	//https://yukicoder.me/problems/199
	int N;
	int A[4],B[4];
	scan(N);
	rep(i,N) scan(A[i]);
	rep(i,N) scan(B[i]);
	int siai=kaijo(N)*kaijo(N);
	int Awinnum=0;
	vint Ajun;
	rep(i,N) Ajun.push_back(i);
	do{
		vint Bjun;
		rep(i,N) Bjun.push_back(i);
		do{
			int Awin=0;
			rep(i,N){
				if(A[Ajun[i]]>B[Bjun[i]]) Awin++;
			}
			if(Awin>N/2) Awinnum++;
		}while(next_permutation(Bjun.begin(),Bjun.end()));
	}while(next_permutation(Ajun.begin(),Ajun.end()));
	double ans=(double)Awinnum/siai;
	prin(ans);
	return 0;
}