#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep3(i, l, n) for (int i = l; i < n; ++i)
#define chmax(a, b) a = (a >= b ? a : b)
#define chmin(a, b) a = (a <= b ? a : b)
#define out(a) cout << a << endl
#define outa(a, n) rep(_, n) cout << a[_] << " "; cout << endl
#define SZ(v) (int)v.size()
#define inf (int)(1e9+7)
#define abs(x) (x >= 0 ? x : -(x))
#define ceil(a, b) a / b + !!(a % b)
#define FIX(a) fixed << setprecision(a)

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<int> a, b;
    rep(i, n) { int tmp; cin >> tmp; a.eb(tmp); }
    rep(i, n) { int tmp; cin >> tmp; b.eb(tmp); }
    sort(all(a));
    sort(all(b));
    int sum = 0;
    do {
        do {
            int c = 0;
            rep(i, n) if (a[i] > b[i]) c++; else if (a[i] < b[i]) c--;
            if (c > 0) sum++;
        } while (next_permutation(all(b)));
    } while (next_permutation(all(a)));
    int kai = 1;
    rep(i, n) kai *= i + 1;
    // out(sum << " " << kai);
    out((double)sum / pow(kai, 2));
}