#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;

int main(){

    int N, idx;
    long double ans=0, pr;
    cin >> N;
    vector<long 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<long double, int>> que;
    for (int i=0; i<N; i++){
        que.push({p[i]*q[i], i});
    }

    for (int i=1; i<=1000000; i++){
        tie(pr, idx) = que.top();
        que.pop();
        ans += pr * i;
        que.push({pr*(1.0-q[idx]), idx});
    }

    cout << setprecision(18) << ans << endl;

    return 0;
}