#include<bits/stdc++.h>

using namespace std;

#define rep(i, n) for (int i = 0; i < n; i++)
#define reps(i, n, m) for (int i = n; i < m; i++)

int main()
{
	int N;
	cin >> N;
	int A[4];
	int b[4];
	rep(i, N) cin >> A[i];
	rep(i, N) cin >> b[i];
	sort(A, A+N);
	sort(b, b+N);
	double res = 0;
	double cnt = 0;
	do {
		int B[4];
		rep(i, N) B[i] = b[i];
		do {
			int ac = 0;
			int bc = 0;
			rep(i, N) {
				if (A[i] > B[i]) ac++;
				else bc++;
			}
			if (ac > bc) res++;
			cnt++;
		} while (next_permutation(B, B+N));
	} while (next_permutation(A, A+N));
	cout << fixed << setprecision(10) << res / cnt << endl;
}