#include <bits/stdc++.h>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

int N, T;
double pa, pb;
int A[22], B[22];
int awins, sum;

default_random_engine gene;
uniform_real_distribution<double> dist(0,1);

vector<int> getrandvec(double p) {
	int x;
	vector<int> v,r;
	rep(i, N) v.push_back(i);

	rep(i, N-1) {
		double d = dist(gene);
		if(d < p) x = 0;
		else x = 1+(N-1-i)*(d-p) / (1-p);
		r.push_back(v[x]);
		v.erase(v.begin()+x);
	}
	r.push_back(v[0]);
	return r;
}

int main() {

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

	rep(_, 300000) {
		sum++;
		vector<int> va(getrandvec(pa)), vb(getrandvec(pb));
		int ascore = 0;
		rep(i, N) {
			if(A[va[i]] <= B[vb[i]]) { continue; }
			ascore += A[va[i]] + B[vb[i]];
		}
		if(ascore > T/2) { awins++; }
	}

	printf("%.10f\n", (double)awins/sum);

	return 0;
}