#pragma GCC optimize("Ofast")
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
#include <deque>
#include <stack>
#include <sstream>
#include <utility>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <tuple>
#include <array>
#include <bitset>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline ll time() {
    return static_cast<long double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n; cin >> n;
    vector<double> p(n),q(n);
    for(int i=0;i<n;i++){
        int x; cin >> x;
        p[i] = x/1000.0;
    }
    for(int i=0;i<n;i++){
        int x; cin >> x;
        q[i] = x/100.0;
    }
    const int k = 100000;
    vector<double> s(k);
    s[0] = 1;
    double res = 1;
    priority_queue<pair<double,double>> pq;
    for(int i=0;i<n;i++){
        pq.push({p[i]*q[i],q[i]});
    }
    for(int i=1;i<k;i++){
        auto p = pq.top(); pq.pop();
        s[i] = s[i-1] - p.first;
        res += s[i];
        p.first *= (1-p.second);
        pq.push(p);
    }
    printf("%.9f\n",res);
}