#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
using namespace std;

#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,(int)(n)-1,0)
#define REP(i,s,e) for (i = s; i <= e; i++)
#define rep(i,n) REP(i,0,(int)(n)-1)
#define INF 100000000

typedef long long ll;

int main() {
    int i, N;
    double P[1000], Q[1000];
    double ans = 0;
    priority_queue<pair<double,int>> q;
    cin >> N;
    rep (i,N) {
        cin >> P[i];
        P[i] /= 1000;
    }
    rep (i,N) {
        cin >> Q[i];
        Q[i] /= 100;
    }
    rep (i,N) q.push(make_pair(P[i]*Q[i],i));
    for (i = 1;; i++) {
        double x = q.top().first;
        int y = q.top().second;
        q.pop();
        ans += i * x;
        q.push(make_pair(x*(1-Q[y]),y));
        if (i * x < 0.00001)
            break;
    }
    cout << ans << endl;
    return 0;
}