#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

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);
	for (int i = 0; i < N; i++)
		a[i] = i;
	int tot = 0, win = 0;
	do {
		vector<int> b(N);
		for (int i = 0; i < N; i++)
			b[i] = i;
		do {
			int cnt = 0;
			for (int i = 0; i < N; i++)
				if (A[a[i]] > B[b[i]])
					cnt++;
			if (cnt > N / 2) win++;
			tot++;
		} while (next_permutation(b.begin(), b.end()));
	} while (next_permutation(a.begin(), a.end()));
	printf("%.10f\n", (double)win / tot);
}