#include <bits/stdc++.h>
using namespace std;
using ll=long long;
ll I=167167167167;
ll Q=1e9+7;


int main() {
	int N,A=1,L=0;
	cin>>N;
	vector<ll> a(N);
	vector<ll> b(N);
	for(int i=0;i<N;i++) cin>>a[i];
	for(int i=0;i<N;i++) cin>>b[i],A*=(i+1);
	sort(a.begin(),a.end());
	sort(b.begin(),b.end());
	for(int i=0;i<A;i++){
		vector<ll> p=b;
		for(int j=0;j<A;j++){
			ll Z=0;
			for(int k=0;k<N;k++){
				if(a[k]>p[k]) Z++;
				if(a[k]<p[k]) Z--;
			}
			if(Z>0) L++;
			next_permutation(p.begin(),p.end());
		}
		next_permutation(a.begin(),a.end());
	}
	long double X=A*A,Y=L;
	cout<<fixed<<setprecision(15);
	cout<<Y/X<<endl;
}