#include <bits/stdc++.h>

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

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;

double p[1111], q[1111], r[1111];

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> p[i];
        p[i] /= 1000.;
    }
    for (int i = 0; i < n; i++) {
        cin >> q[i];
        q[i] /= 100.;
    }
    priority_queue<pair<double, int> > que;
    for (int i = 0; i < n; i++) {
        que.push(make_pair(p[i]*q[i], i));
    }
    double ans = 0;
    for (int i = 1; i < 1000000; i++) {
        auto now = que.top(); que.pop();
        ans += now.first * i;
        double next = now.first * (1-q[now.second]);
        que.push(make_pair(next, now.second));
    }
    printf("%.10lf\n", ans);
    return 0;
}