#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<string>
#include<iomanip>
#include<numeric>
#include<queue>
#include<deque>
#include<stack>
#include<set>
#include<map>
using namespace std;
typedef long long ll;
const int mod=998244353;
int main(){
	int n,a[4],b[4];
	cin>>n;
	for(int i=0;i<n;i++)
		cin>>a[i];
	for(int i=0;i<n;i++)
		cin>>b[i];
	sort(a,a+n);
	sort(b,b+n);
	double ans=0;
	do{
		do{
			int cnt=0;
			for(int i=0;i<n;i++)
				if(a[i]>b[i])
					cnt++;
			if(cnt>n-cnt)
				ans++;
		}while(next_permutation(b,b+n));
	}while(next_permutation(a,a+n));
	for(int i=1;i<=n;i++)
		ans/=i*i;
	cout<<fixed<<setprecision(20)<<ans<<endl;
}