#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <assert.h>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

int main() {

  int N; cin >> N;
  double p[N], q[N];
  rep(i, N) cin >> p[i], p[i] /= 1000;
  rep(i, N) cin >> q[i], q[i] /= 100;

  priority_queue<double> pq;
  rep(k, 100) {
    rep(i, N) {
      pq.emplace(p[i] * pow(1-q[i], k) * q[i]);
    }
  }

  double res = 0.0;
  int cnt = 1;
  while(!pq.empty()) {
    res += (cnt++) * pq.top(); pq.pop();
  }

  cout << setprecision(6) << res << endl;

  return 0;
}