#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;

int main(){
    int N;
    cin >> N;
    int A[N];
    int B[N];
    for(int i=0;i<N;i++){
        cin >> A[i];
    }
    for(int i=0;i<N;i++){
        cin >> B[i];
    }
    sort(A,A+N);
    sort(B,B+N);
    int cnt=0;
    int all=0;
    do{
        int tmp=0;
        for(int i=0;i<N;i++){
            if(A[i]>B[i]) tmp++;
        }
        if(tmp>(N/2)) cnt++;
        all++;
    }while(next_permutation(A,A+N));
    double ans=cnt*1.0/all;
    printf("%.5f\n",ans);
}