#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int main() {
	int n; cin >> n;
	vector<double> p(n), q(n);
	for (int i = 0; i < n; i++) {
		cin >> p[i];
		p[i] /= 1000;
	}
	for (int i = 0; i < n; i++) {
		cin >> q[i];
		q[i] /= 100;
	}
	double e = 0;
	for (int t = 1; t <= 500000; t++) {
		int _i = 0;
		for (int i = 0; i < n; i++)
			if (p[i] * q[i] > p[_i] * q[_i])
				_i = i;
		e += p[_i] * q[_i] * t;
		p[_i] *= 1 - q[_i];
	}
	cout << e << endl;
}