#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>
#include<limits>

#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ll, string> pls;

int main()
{
	int N;  cin >> N;
	vector<int> A(N), B(N);
	
	ll sum = 1,num;
	for (int i = 1; i <= N; i++) {
		sum *= i;
	}
	num = sum;
	sum *= sum;

	for (int i = 0; i < N; i++)  cin >> A[i];
	for (int i = 0; i < N; i++)  cin >> B[i];

	ll Win = 0;
	do {
		int i = 0,win = 0,lose = 0;
		for (auto x : B) {
			if (A[i] > x)win++;
			else if (A[i] < x)lose++;
			i++;
		}
		if (win > lose)Win++;
	} while (next_permutation(B.begin(), B.end()));

	Win *= num;

	double ans;
	if (Win == 0)ans = 0;
	else ans = (double)Win / sum;

	printf("%.10f\n",ans);
	return	0;
}