#include <bits/stdc++.h>
using namespace std;

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;
    }

    priority_queue<pair<double, int>> que;
    for (int i = 0; i < N; i++) {
        que.push({P[i] * Q[i], i});
    }

    double ans = 0;
    int num = 1;
    while (num < 1e7) {
        auto p = que.top();
        que.pop();
        ans += num * p.first;
        p.first *= (1 - Q[p.second]);
        que.push(p);
        num++;
    }
    cout << fixed << setprecision(4) << ans << endl;
}