#include<iostream>
#include<vector>
#include<set>
#include<map>
#include<list>
#include<stack>
#include<queue>
#include<bitset>
#include<array>
#include<algorithm>
#include<cstdio>
#include<string>
#include<cstdlib>
#include<numeric>
#define D long long
#define U unsigned
#define SHIKOU 3000000
using namespace std;
D n, m,a, b, d, e, x, y, z;
D i, j, k;
char c,f;
string s;
struct Prob {
	double p;
	double q;
	double r;
	bool operator<(const Prob &obj)const {
		return r < obj.r;
	}
	bool operator>(const Prob &obj)const {
		return r > obj.r;
	}
};
double kitai[SHIKOU];
double ans;
int main() {
	D t;
	priority_queue<Prob> p;
	Prob tmp[1000],tm;
	cin >> a;
	for (i = 0; i < a; i++) {
		cin >> tmp[i].p;
		tmp[i].p /= 1000.0;
	}
	for (i = 0; i < a; i++) {
		cin >> tmp[i].q;
		tmp[i].q /= 100.0;
	}
	for (i = 0; i < a; i++)
		tmp[i].r = tmp[i].p * tmp[i].q;
	for (i = 0; i < a; i++)
		p.push(tmp[i]);
	for (i = 0; i < SHIKOU; i++) {
		tm = p.top();
		p.pop();
		kitai[i] +=tm.r;
		tm.p *= 1.0 - tm.q;
		tm.r = tm.p*tm.q;
		p.push(tm);
	}
	for (i = 0; i < SHIKOU; i++)
		ans += (double)i*kitai[i];
	printf("%.6f\n", ans+1);
}