#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a, b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define pb push_back
#define show(x) cout <<#x<<" = "<<(x)<<endl
#define spair(p) cout <<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout <<" "<<kbrni;cout<<endl

using namespace std;

typedef pair<double,int>P;

const int MAX_N = 100005;

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    vector<double> p(n);
    vector<double> q(n);
    rep(i,n){
        cin >> p[i];
        p[i] /= 1000;
    }
    rep(i,n){
        cin >> q[i];
        q[i] /= 100;
    }
    priority_queue<P> que;
    rep(i,n){
        que.push(P(p[i]*q[i],i));
    }
    double prob = 0;
    double ans = 0;
    rep(i,100005){
        P a = que.top();
        que.pop();
        ans += 1-prob;
        prob += a.fi;
        que.push(P(a.fi*(1-q[a.se]),a.se));
    }
    printf("%.10lf\n",ans);
    return 0;
}