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

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);

    int N; cin >> N;
    vector<int> A(N),B(N);
    rep(i,N) cin >> A[i];
    sort(A.begin(), A.end());
    rep(i,N) cin >> B[i];
    int ans = 0;
    do{
        int Awin = 0;
        rep(i,N) Awin += (A[i] > B[i]);
        if(Awin > N / 2) ans++;
    }while(next_permutation(A.begin(), A.end()));

    double res = (double)ans;
    rep(i,N) res /= (double)(i+1);
    cout.precision(17);
    cout << res << endl;
}