#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

size_t factorial(size_t a) {
	size_t tmp = 1;
	for (size_t i = 2; i <= a; ++i) tmp *= i;
	return tmp;
}

int main() {
	double sum = 0;
	size_t N, tmp;
	cin >> N;
	vector<int> A(N), B(N);
	for (size_t i = 0; i < N; ++i) cin >> A[i];
	for (size_t i = 0; i < N; ++i) cin >> B[i];
	sort(A.begin(), A.end());
	do {
		sort(B.begin(), B.end());
		do {
			tmp = 0;
			for (size_t i = 0; i < N; ++i) {
				if (A[i] > B[i]) ++tmp;
			}
			if (tmp > N / 2) ++sum;
		} while (next_permutation(B.begin(), B.end()));
	} while (next_permutation(A.begin(), A.end()));
	tmp = factorial(N);
	cout << sum / tmp / tmp;
}