#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N; cin >> N;
    vector<int> A(N),B(N);
    for(auto &a : A) cin >> a;
    for(auto &b : B) cin >> b;

    vector<int> P(N);
    iota(P.begin(),P.end(),0);
    int all = 0,win = 0;
    do{
        vector<int> Q(N);
        iota(Q.begin(),Q.end(),0);
        do{
            int ok = 0;
            for(int i=0; i<N; i++) ok += A.at(P.at(i))>B.at(Q.at(i));
            if(ok+ok > N) win++;
            all++;

        }while(next_permutation(Q.begin(),Q.end()));
    }while(next_permutation(P.begin(),P.end()));
    cout << fixed << setprecision(20) << win/(all+0.0) << endl;
}