#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

struct Node {
  int id;
  double rate;

  Node(int id = -1, double rate = -1) {
    this->id = id;
    this->rate = rate;
  }

  bool operator>(const Node &n) const {
    return rate < n.rate;
  }
};

int main() {
  int N;
  cin >> N;
  vector<int> P(N);
  vector<int> Q(N);

  for (int i = 0; i < N; ++i) {
    cin >> P[i];
  }

  for (int i = 0; i < N; ++i) {
    cin >> Q[i];
  }

  priority_queue <Node, vector<Node>, greater<Node>> pque;
  for (int i = 0; i < N; ++i) {
    int p = P[i];
    int q = Q[i];
    double rate = (p * 1.0 / 1000) * (q * 1.0 / 100);
    pque.push(Node(i, rate));
  }

  double ans = 0.0;

  for (int t = 1; t <= 1000000 && not pque.empty(); ++t) {
    Node node = pque.top();
    pque.pop();

    if (node.rate <= 0.0) continue;

    ans += t * node.rate;
    node.rate *= (1.0 - Q[node.id] * 1.0 / 100);
    pque.push(node);
  }

  cout << fixed << setprecision(10) << ans << endl;

  return 0;
}