#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define INF 1e9
#define MOD 1000000007
#define ALL(v) v.begin(), v.end()
#define P pair<ll, ll>
using namespace std;
typedef long long ll;
int dy[] = {0, 0, 1, -1, 1, 1, -1, -1};
int dx[] = {1, -1, 0, 0, 1, -1, 1, -1};

int main()
{
    ll N;
    cin >> N;
    vector<ll> A(N);
    vector<ll> B(N);
    REP(i, N) {
        cin >> A[i];
    }
    REP(i, N) {
        cin >> B[i];
    }
    vector<ll> indexA(N);
    vector<ll> indexB(N);
    iota(ALL(indexA), 0);
    iota(ALL(indexB), 0);
    ll win_cnt = 0;
    ll all_cnt = 0;
    do
    {
        do {
            all_cnt++;
            ll cnt = 0;
            REP(i, N)
            {
                if (A[indexA[i]] > B[indexB[i]]) {
                    cnt++;
                }
            }
            if (cnt > N/2)
                win_cnt++;
        } while (next_permutation(ALL(indexB)));
    } while (next_permutation(ALL(indexA)));
    cout << setprecision(20) << (double)win_cnt / all_cnt << endl;
    return 0;
}