#include <bits/stdc++.h>
#define FOR(i,a,b) for (int (i) = (a); (i) < (b); ++(i))
#define rep(i,n) for (int (i) = 0; (i) < (n); ++(i))
#define rrep(i,n) for (int (i) = (n); (i) >= 0; --(i))
#define all(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
const int INF = 1e9;
const ll LINF = 1LL << 60;
const ll MOD = 1e9 + 7;

int N, A[4], B[4];

int main() {
    cin >> N;
    rep(i,N) cin >> A[i];
    rep(i,N) cin >> B[i];
    sort(A, A+N);
    sort(B, B+N);
    int awin = 0;
    int ap = 0;
    do {
        do {
            ++ap;
            rep(i,N) {
                if (A[i] > B[i]) ++awin;
            }
        } while (next_permutation(B, B+N));
    } while (next_permutation(A, A+N));
    double p = (double)awin / (double)ap - 1.0;
    cout << fixed << setprecision(10) << p << "\n";
    return 0;
}