/* -*- coding: utf-8 -*-
 *
 * 210.cc: No.210 探し物はどこですか? - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 1000;

/* typedef */

typedef pair<double,int> pdi;

/* global variables */

int ps[MAX_N], qs[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> ps[i];
  for (int i = 0; i < n; i++) cin >> qs[i];

  priority_queue<pdi> q;

  for (int i = 0; i < n; i++)
    q.push(pdi((double)ps[i] * qs[i] / 100000, i));

  double esum = 0.0;
  int k = 1;

  for (;;) {
    pdi u = q.top(); q.pop();
    double &pq = u.first;
    int &i = u.second;
    if (pq < 1e-10) break;

    esum += k * pq;
    k++;
    double pq0 = pq * (100 - qs[i]) / 100;
    q.push(pdi(pq0, i));
  }

  printf("%.6lf\n", esum);
  return 0;
}