#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T> V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> > Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T> mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }

/*
 <url:https://yukicoder.me/problems/no/210>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

typedef long double ld;
ld solve(){
    ld res = 0;
    int n; cin >> n;
    vector<ld> p(n),q(n);
    for(auto& in:p){ cin >> in; in/=1000.0;}
    for(auto& in:q){ cin >> in; in/=100.0; }
    priority_queue<pair<ld,int>> pq;
    for(int i = 0; i < n;i++) pq.push(make_pair(p[i]*q[i],i));
    int kassa = 0;
    while(kassa++<1000000){
        ld P; int ind; tie(P,ind) = pq.top(); pq.pop();
        res += kassa*P;
        P *= 1-q[ind];
        pq.push(make_pair(P,ind));
    }
    return res;
}
int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(12) << solve() << endl;
    return 0;
}