#include <cstdio>
#include <vector>
#include <algorithm>
#include <array>
#include <set>
#include <map>
#include <queue>
#include <tuple>
#include <unordered_set>
#include <unordered_map>
#include <functional>
#include <cassert>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
#define repeat_from(i,m,n) for (int i = (m); (i) < (n); ++(i))
#define repeat_reverse(i,n) for (int i = (n)-1; (i) >= 0; --(i))
#define repeat_from_reverse(i,m,n) for (int i = (n)-1; (i) >= (m); --(i))
#define whole(f,x,...) ([&](decltype((x)) y) { return (f)(begin(y), end(y), ## __VA_ARGS__); })(x)
typedef long long ll;
using namespace std;
template <class T> void setmax(T & a, T const & b) { if (a < b) a = b; }
template <class T> void setmin(T & a, T const & b) { if (b < a) a = b; }
template <typename T, typename X> auto vectors(T a, X x) { return vector<T>(x, a); }
template <typename T, typename X, typename Y, typename... Zs> auto vectors(T a, X x, Y y, Zs... zs) { auto cont = vectors(a, y, zs...); return vector<decltype(cont)>(x, cont); }
int main() {
    // input
    int n; scanf("%d", &n);
    vector<int> p(n); repeat (i,n) scanf("%d", &p[i]);
    vector<int> q(n); repeat (i,n) scanf("%d", &q[i]);
    // compute
    vector<long double> r(n); repeat (i,n) r[i] = (p[i] / 1000.) * (q[i] / 100.);
    auto cmp = [&](int i, int j) { return r[i] < r[j]; };
    priority_queue<int, vector<int>, decltype(cmp)> que(cmp);
    repeat (i,n) que.push(i);
    long double ans = 0;
    const long double eps = 1e-16;
    for (int k = 1; ; ++ k) {
        int i = que.top(); que.pop();
        if (r[i] < eps) break;
        ans += k * r[i];
        r[i] *= 1 - q[i] / 100.;
        que.push(i);
    }
    // output
    printf("%.6Lf\n", ans);
    return 0;
}