#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pii = pair<int, int>;
using pdd = pair<ld, ld>;
using pll = pair<ll, ll>;
using pli = pair<ll, int>;
using pil = pair<int, ll>;
template <typename T>
using Graph = vector<vector<T>>;
const int MOD = 1e9 + 7;
const ld PI = acos(-1);

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    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> v(2 * N);
    iota(v.begin(), v.begin() + N, 0);
    iota(v.begin() + N, v.end(), 0);
    int ans = 0;
    do {
        do {
            int cnt = 0;
            for (int i = 0; i < N; ++i) {
                cnt += (A[v[i]] > B[v[i + N]] ? 1 : -1);
            }
            if (cnt > 0)
                ans++;
        } while (next_permutation(v.begin() + N, v.end()));
    } while (next_permutation(v.begin(), v.begin() + N));

    int fac = 1;
    for (int i = 1; i <= N; ++i) {
        fac *= i * i;
    }

    cout << fixed << setprecision(10) << (ld)ans / fac << endl;

    return 0;
}