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

#include <queue>
#include <cstdio>
inline int getInt(){ int s; scanf("%d", &s); return s; }

#include <set>

using namespace std;

int main(){
  const int n = getInt();
  vector<int> p(n);
  vector<int> q(n);

  REP(i,n) p[i] = getInt();
  REP(i,n) q[i] = getInt();

  priority_queue<pair<double, double> > pq;

  REP(i,n) pq.push(make_pair(p[i] / 1000.0 * q[i] / 100.0, q[i] / 100.0));

  double ans = 0;
  REP(i,500000){
    const pair<double, double> d = pq.top(); pq.pop();
    ans += (i + 1) * d.first;
    pq.push(make_pair(d.first * (1 - d.second), d.second));
  }

  printf("%.10f\n", ans);
  return 0;
}