#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <set>
using namespace std;

int main(){
	int n;
	cin >> n;
	vector<double> p(n), q(n);
	const double p_ = 1.0/1000;
	const double q_ = 1.0/100;

	for(int i=0; i<n; i++){
		int tmp;
		cin >> tmp;
		p[i] = tmp * p_;
	}
	for(int i=0; i<n; i++){
		int tmp;
		cin >> tmp;
		q[i] = tmp * q_;
	}

	double ans = 0.0;

	priority_queue<pair<double, pair<double,int>>> pq;
	for(int i=0; i<n; i++){
		pq.push({p[i] * q[i], {p[i], i}});
	}

	for(int i=1; i<=1000000; ++i){
		auto val = pq.top(); pq.pop();
		ans += i * val.first;
		double p_next = val.second.first * (1.0 - q[val.second.second]);
		pq.push({p_next * q[val.second.second], {p_next, val.second.second}});
	}

	printf("%.16f\n", ans);
	return 0;
}