#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0;i < (n); ++i)
#define all(v) (v).begin(), (v).end()
using ll = long long;

int upstairs(int x) {
    if (x == 0) return 1;
    else return x * upstairs(x - 1);
}

int main() {
    int n, cnt = 0;
    cin >> n;
    vector<int> a(n), b(n);

    rep(i, n) cin >> a[i];
    rep(i, n) cin >> b[i];

    sort(all(a));
    sort(all(b));

    do {
        do {
            int acnt = 0, bcnt = 0;
            rep(i, n) {
                if(a[i] > b[i]) ++acnt;
                else if (a[i] < b[i]) ++bcnt;
            }
            if (acnt > bcnt) ++cnt;
        } while(next_permutation(all(b)));
    } while(next_permutation(all(a)));

    double ans;
    ans = cnt / pow(upstairs(n), 2);

    cout << ans << endl;

    return 0;
}