#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	cin >> n;
	vector<double> p(n), q(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.emplace(p[i] * q[i], i);
	}

	double E = 0;
	for (int i = 1; i < 1000000; i++) {
		double x;
		int y;
		tie(x, y) = que.top(); que.pop();
		E += i * x;
		que.emplace(x * (1 - q[y]), y);
	}

	printf("%.20f\n", E);
}