#include "bits/stdc++.h"
#include<unordered_map>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
template<class T>
using Table = vector<vector<T>>;

//vector<vector<ld>>pers(1000, vector<ld>(5000));

vector<double>pers;
int main() {
	int N; cin >> N;
	vector<double>ps,qs;
	for (int i = 0; i < N; ++i) {
		double p; cin >> p;
		p /= 1000;
		ps.push_back(p);
	}
	for (int i = 0; i < N; ++i) {
		double q; cin >> q;
		q /= 100;
		qs.push_back(q);
	}
	for (int i = 0; i < N; ++i) {
		ld now = ps[i];
		for (int j = 0; j < 5000; ++j) {
			pers.push_back(now*qs[i]);
			now -= now*qs[i];
		}
	}
	sort(pers.begin(), pers.end(),greater<ld>());
	ld ans = 0;
	for (int i = 0; i < pers.size(); ++i) {
		ans += pers[i] * (i + 1);
	}
	cout << fixed<<setprecision(22)<<ans << endl;
	return 0;
}