#define _CRT_SECURE_NO_WARNINGS
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<vector>
#include<queue>
using namespace std;
const int maxn = 1e6;
double p[1005], dp[1005],q[1005];
int n;
typedef struct Value{
	double v;
	int x;
	Value(double v = 0, int x = 0) :v(v), x(x){}
	friend bool operator < (Value a, Value b){
		return a.v < b.v;
	}
}Value;
priority_queue<Value> Q;
double v(int x){
	return p[x] * (1 - dp[x]) * q[x];
}
int main(){
	cin >> n;
	for (int i = 0; i < n; i++){
		scanf("%lf", &p[i]);
		p[i] /= 1e3;
	}
	for (int i = 0; i < n; i++){
		scanf("%lf", &q[i]);
		q[i] /= 1e2;
	}
	double g = 0;
	for (int i = 0; i < n; i++) Q.push(Value(v(i), i));
	for (int i = 1; i < maxn; i++){
		if (i%10000 == 0){
			int k = 0;
		}
		int x = Q.top().x;
		Q.pop();
		g += i * v(x);
		dp[x] += (1 - dp[x]) * q[x];
		Q.push(Value(v(x), x));
	}
	printf("%.7lf\n", g);
	return 0;
}