#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;

const static int NIL = -1;
const long long INF = 1LL << 60;
typedef long long ll;
typedef unsigned long long ull;

bool is_debug = false;
int ini = 1000000001;
ull mod = 1000000007;

int main(){
	int n;
	cin >> n;
	vector<int> a(n);
	vector<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.begin(), a.end());
	sort(b.begin(), b.end());
	int all = 0;
	int win = 0;
	do{
		do{
			all++;
			int cnt = 0;
			for(int i = 0; i < n; i++){
				if(a[i] > b[i])cnt++;
			}
			if(cnt * 2 > n)win++;
		}while(next_permutation(b.begin(), b.end()));
	}while(next_permutation(a.begin(), a.end()));

	
	cout << setprecision(10) << (double)win / all << endl;
	
}