#include <bits/stdc++.h>
#define NIL (-1)
#define ll long long
#define all(x) (x).begin(),(x).end()
using namespace std;
const double PI = acos(-1.0);

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

	vector<int> a(N), b(N);
	for (int i = 0; i < N; i++) a[i] = b[i] = i;

	int ret = 0;
	int tot = 0;
	do {
		do {
			tot++;
			int co = 0;
			for (int i = 0; i < N; i++) {
				if (A[a[i]] > B[b[i]]) co++;
			}
			if (co * 2 > N) ret++;
		} while (next_permutation(all(b)));
	} while (next_permutation(all(a)));

	cout << fixed << setprecision(10) << (double)ret / tot << endl;
}