#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    int n;
    cin >> n;
    vector<double> p(n), q(n);
    priority_queue<pair<double, int> > pq;
    for(int i=0; i<n; ++i){
        cin >> p[i];
        p[i] /= 1000.0;
    }
    for(int i=0; i<n; ++i){
        cin >> q[i];
        q[i] /= 100.0;
        pq.push(make_pair(p[i] * q[i], i));
    }

    double ans = 0.0;
    for(int i=1; i<=10000000; ++i){
        double x = pq.top().first;
        int k = pq.top().second;
        pq.pop();

        ans += x * i;
        x *= 1 - q[k];
        pq.push(make_pair(x, k));
    }
    printf("%.10f\n", ans);

    return 0;
}