#include <bits/stdc++.h>

using namespace std;

namespace {

    typedef double real;
    typedef long long ll;

    template<class T> ostream& operator<<(ostream& os, const vector<T>& vs) {
        if (vs.empty()) return os << "[]";
        auto i = vs.begin();
        os << "[" << *i;
        for (++i; i != vs.end(); ++i) os << " " << *i;
        return os << "]";
    }
    template<class T> istream& operator>>(istream& is, vector<T>& vs) {
        for (auto it = vs.begin(); it != vs.end(); it++) is >> *it;
        return is;
    }

    int N;
    vector<real> P, Q;
    void input() {
        cin >> N;
        P.resize(N); Q.resize(N);
        for (int i = 0; i < N; i++) {
            real p; cin >> p; p /= 1000;
            P[i] = p;
        }
        for (int i = 0; i < N; i++) {
            real q; cin >> q; q /= 100;
            Q[i] = q;
        }
    }

    struct S : pair<real, int> {
        S(real a, int b) : pair<real,int>(a, b) {}
        bool operator<(const S& o) const {
            return first * Q[second] < o.first * Q[o.second];
        }
    };

    void solve() {
        priority_queue<S> PQ;
        for (int i = 0; i < N; i++) PQ.emplace(P[i], i);
        real ans = 1.0;
        real mother = 1.0;
        for (int t = 1; t <= 1000; t++) {
            auto pi = PQ.top(); PQ.pop();
            real p = pi.first;
            real index = pi.second;
            real q = Q[index];
            mother -= p * q;
            real np = p * (1.0 - q);
            ans += mother;
            PQ.emplace(np, index);
        }
        printf("%.12f\n", ans);
    }
}

int main() {
    input(); solve();
    return 0;
}