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

int main(){
    int N; cin >> N;
    vector<int> A(N), B(N);
    for(int &x: A)cin >> x;
    for(int &x: B)cin >> x;
    sort(A.begin(), A.end());
    sort(B.begin(), B.end());
    double awin = 0, game = 0;;
    do{
        do{
            int a = 0;
            for(int i = 0; i < N; i++)if(A[i] > B[i])a++;
            if(a > N / 2)awin++;
            game++;
        }while(next_permutation(B.begin(), B.end()));
    }while(next_permutation(A.begin(), A.end()));
    double pa = awin / game;
    cout << fixed << setprecision(10) << pa << endl;
}