#include <bits/stdc++.h>

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)
#define unless(p) if(!(p))
#define until(p) while(!(p))

using ll = std::int64_t;
using P = std::tuple<int,int>;

int N;
double p[1000], q[1000], r[1000];

double rec(int t){
    if(t >= 10000){
        return 0;
    }

    int i = std::max_element(r, r + N) - r;
    double ri = r[i];

    if(ri == 1){
        return 1;
    }

    for(int j=0;j<N;++j){
        r[j] *= 1.0 / (1.0 - ri);
    }

    r[i] *= (1.0 - q[i]);

    return 1.0 + (1.0 - ri) * rec(t + 1);
}

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    std::cin >> N;

    for(int i=0;i<N;++i){
        std::cin >> p[i];
        p[i] *= 1e-3;
    }

    for(int i=0;i<N;++i){
        std::cin >> q[i];
        q[i] *= 1e-2;
    }

    for(int i=0;i<N;++i){
        r[i] = p[i] * q[i];
    }

    double e = rec(0);
    printf("%.5f\n", e);
}