#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <queue>
#include <stack>
#include <set>
#include <map>

#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
typedef long long ll;

using namespace std;


int inputValue(){
    int a;
    cin >> a;
    return a;
};

template <typename T>
void output(T a, int precision) {
    if(precision > 0){
        cout << fixed << setprecision(precision)  << a << "\n";
    }
    else{
        cout << a << "\n";
    }
}

int main() {
    
    // source code
    int N = inputValue();
    vector<double> P(N), Q(N);
    
    rep(i, N){
        P[i] = (double)inputValue() / 1000.0;
    }
    rep(i, N){
        Q[i] = (double)inputValue() / 100.0;
    }
    
    priority_queue<double> pq;
    
    vector<double> R(N);
    rep(j, N){
        R[j] = P[j] * Q[j];
        pq.push(R[j]);
    }
    
    rep(i, 5000){
        rep(j, N){
            pq.push(R[j] * (1 - Q[j]));
            R[j] = R[j] * (1 - Q[j]);
        }
    }
    
    int cnt = 1;
    double ret = 0;
    while (!pq.empty()) {
        double t = pq.top();
        pq.pop();
        
        ret += t * cnt;
        cnt++;
    }
    
    output(ret, 5);
    
    return 0;
}