#include <bits/stdc++.h>
using namespace std;

int n;
double p = 0;

int main()
{
	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];

	sort(b.begin(), b.end());

	do {
		int k = 0, i = 0;

		for (vector<int>::iterator itr = b.begin(); itr != b.end(); itr++) {
			if (a[i] > *itr)
				k++;

			i++;
		}

		if (k > n / 2)
			p++;
	
	} while (next_permutation(b.begin(), b.end()));

	for (int i = 1; i <= n; i++)
		p /= (double)i;

	cout << p << endl;
}