#include<bits/stdc++.h>
using namespace std;
using ll = long long;
const int MOD = 1e9+7;
const int INF = 1e9;
const ll INFll = 1e18;
#define put(n) cout<<(n)<<endl
#define Cout(n) cout<<(n)
#define rep(i,num,N) for(int(i)=(num);(i)<(N);++(i))
#define rrep(i,num,N) for(int (i)=(num);(i)>(N);--(i))
#define all(v) (v).begin() , (v).end()
#define rall(v) (v).rbegin() , (v).rend()
#define MP make_pair
#define pb(q) push_back(q)
int dx[4] = {0,0,1,-1};
int dy[4] = {1,-1,0,0};


int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int N;
    cin>>N;
    vector<int> A(N);
    vector<int> B(N);

    rep(i,0,N) cin>>A[i];
    rep(i,0,N) cin>>B[i];

    sort(all(A));
    sort(all(B));

    double cnt = 0.0;
    double ans = 0.0;
    
    do{
        int win = 0;
        rep(i,0,N){
            if(A[i] > B[i]) ++win;
        }
        if(win >= N/2+1) ans += 1.0;
        cnt += 1.0;
        
    }while(next_permutation(all(A)));

    cout << fixed << setprecision(10) << ans/cnt << endl;
}