#include <bits/stdc++.h>
#define _USE_MATH_DEFINES
#include <math.h>
#include <algorithm>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define print(s) cout << s << endl
#define acc(v) accumulate(v.begin(), v.end(), 0)

using namespace std;
typedef long long ll;
const int INF = 1e9;
const ll LINF = 1e18;
const ll MOD = 1e9 + 7;
typedef pair<int, int> pii;
typedef vector<int> vint;
typedef vector<string> vstr;
typedef vector<char> vchar;
int main()
{
	int n;
	cin >> n;
	vector<int> a(n), b(n);
	rep(i,n){
		cin >> a[i];
	}
	rep(i,n){
		cin >> b[i];
	}
	sort(all(a));
	double Ans = 0;
	int Count = 0;
	do
	{
		Count++;
		sort(all(b));
		int count = 0;
		double ans = 0;
		do
		{
			int win = 0;
			count++;
			rep(i, n)
			{
				if (a[i] > b[i])
					win++;
			}
			ans += win > n / 2 ? 1 : 0;
		} while (next_permutation(all(b)));
		Ans += 1.0 * ans / count;
	} while (next_permutation(all(a)));
	cout << 1.0 * Ans / Count << endl;

}