#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
using namespace std;
D n, m,a, b, d, e, x, y, z;
D i, j, k;
char c,f;
string s;
double p[1000], q[1000];
double kitai[10000];
double ans;
int main() {
	D t;
	cin >> a;
	for (i = 0; i < a; i++) {
		cin >> p[i];
		p[i] /= 1000;
	}
	for (i = 0; i < a; i++) {
		cin >> q[i];
		q[i] /= 100;
	}
	for (i = 0; i < 10000; i++) {
		b = 0;
		for (j = 1; j < a; j++) {
			if (p[j]*q[j] > p[b]*q[b])
				b = j;
		}
		kitai[i] +=(p[b] * q[b]);
		p[b] *=1 - q[b];
	}
	for (i = 0; i < 10000; i++)
		ans += (double)i*kitai[i];
	printf("%.6f\n", ans+1);
}