#include <iostream>
#include <vector>
#include <algorithm>

#define rep(i, n) for(int i=0; i<n; i++) 

using namespace std;

int N;
vector<int> A;
vector<int> B;
vector<int> C;

int main() {
    cin >> N;
    
    A.resize(N);
    B.resize(N);
    C.resize(N);
    
    rep(i, N) {
        cin >> A[i];
        C[i] = i;
    }
    rep(i, N) {
        cin >> B[i];
    }
    
    int ans_num=0;
    int num=0;
    do {
        int count=0;
        rep(i, N) {
            if(A[C[i]]>B[i]) count++;
        }
        if(count>(N/2)) ans_num++;
        num++;
    } while(next_permutation(C.begin(), C.end()));
    
    cout << (long double)ans_num/(long double)num << endl;
    

    return 0;
    
}