#include<iostream>
#include<iomanip>
#include<cmath>
#include<string>
#include<vector>
#include<list>
#include<algorithm>
#include<map>
#include<set>
#include<queue>
#include<stack>
using namespace std;
typedef long long ll;
#define fi first
#define se second
#define mp make_pair
#define rep(i, n) for(int i=0;i<n;++i)
#define rrep(i, n) for(int i=n;i>=0;--i)
const int inf=1e9+7;
const ll mod=1e9+7;
const ll big=1e18;
const double PI=2*asin(1);

int main() {
    int N;
    cin>>N;
    vector<int> A(N), B(N);
    for(int i=0;i<N;++i){
        cin>>A[i];
    }
    for(int i=0;i<N;++i){
        cin>>B[i];
    }
    sort(A.begin(), A.end());
    sort(B.begin(), B.end());
    double Anum = 0;
    double all = 0;
    int tmpA;
    do{
        do{
            tmpA = 0;
            for(int i=0;i<N;++i){
                if(A[i]>B[i])tmpA++;
            }
            if(tmpA>N/2) Anum++;
            all++;
        }while(next_permutation(B.begin(), B.end()));
    }while(next_permutation(A.begin(), A.end()));
    cout<<setprecision(20)<<Anum/all<<endl;
}