#include <iostream>
#include <vector>
#include <set>
#include <cassert>
#include <algorithm>
using namespace std;

int N, A[5009], R[5009];

int main() {
	// Step #1. Input
	cin >> N;
	for (int i = 0; i < N; i++) cin >> A[i];
	for (int i = 0; i < N; i++) cin >> R[i];
	assert(N <= 20);

	// Step #2. Brute Force
	double Answer = 0.0, Cnts = 0.0;
	for (int i = 0; i < (1 << N); i++) {
		vector<int> S; double E = 0;
		for (int j = 0; j < N; j++) {
			S.push_back(A[j]);
			sort(S.begin(), S.end());
			reverse(S.begin(), S.end());
			if ((i & (1 << j)) != 0) {
				E += 1.0 * S[S.size() - 1] * R[j];
				S.pop_back();
			}
		}
		Answer += E;
		Cnts += 1.0;
	}
	printf("%.12lf\n", Answer / Cnts);
	return 0;
}