#include <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>
using namespace std;
int main(){
    int n;cin>>n;
    vector<int> A(n);
    vector<int> B(n);
    for(int i = 0; n > i; i++){
        cin>>A[i];
    }
    for(int i = 0; n > i; i++){
        cin>>B[i];
    }
    sort(A.begin(),A.end());
    sort(B.begin(),B.end());
    int sm = 0;
    int wn = 0;
    do{
        do{
            int t = 0;
            for(int i = 0; n > i; i++){
                if(A[i] > B[i]){
                    t++;
                }
            }
            if(t > n/2)wn++;
            sm++;
        }while(next_permutation(B.begin(),B.end()));
    }while(next_permutation(A.begin(),A.end()));
    cout << fixed << setprecision(10) << (double)wn/sm << endl;
    
}