#include <bits/stdc++.h>
using namespace std;

// #define int long long
#define rep(i, n) for (long long i = (long long)(0); i < (long long)(n); ++i)
#define reps(i, n) for (long long i = (long long)(1); i <= (long long)(n); ++i)
#define rrep(i, n) for (long long i = ((long long)(n)-1); i >= 0; i--)
#define rreps(i, n) for (long long i = ((long long)(n)); i > 0; i--)
#define irep(i, m, n) for (long long i = (long long)(m); i < (long long)(n); ++i)
#define ireps(i, m, n) for (long long i = (long long)(m); i <= (long long)(n); ++i)
#define irreps(i, m, n) for (long long i = ((long long)(n)-1); i > (long long)(m); ++i)
#define SORT(v, n) sort(v, v + n);
#define REVERSE(v, n) reverse(v, v+n);
#define vsort(v) sort(v.begin(), v.end());
#define all(v) v.begin(), v.end()
#define mp(n, m) make_pair(n, m);
#define cinline(n) getline(cin,n);
#define replace_all(s, b, a) replace(s.begin(),s.end(), b, a);
#define PI (acos(-1))
#define FILL(v, n, x) fill(v, v + n, x);
#define sz(x) (long long)(x.size())

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vs = vector<string>;
using vpll = vector<pair<ll, ll>>;
using vtp = vector<tuple<ll,ll,ll>>;
using vb = vector<bool>;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<class t> using vc=vector<t>;
template<class t> using vvc=vc<vc<t>>;

const ll INF = 1e9+10;
const ll MOD = 1e9+7;
const ll LINF = 1e18;

// k回その部屋を探索して見つけられる確率 p[i]*(1-q[i])^(k-1)*q[i] (徐々に確率は低下していく)
// 各操作回数で、今最も高い確率のものを貪欲に取っていく
// 今の操作回数*最高確率の総和が求めたい期待値
// 最終的にどの部屋の確率も0に近くなっていき、期待値はある値に収束していく
// 操作回数1 * 最高確率 + 操作回数2 * 最高確率' +... + 操作回数n * 最高確率 <- ゼロに近づいていく

signed main()
{
  cin.tie( 0 ); ios::sync_with_stdio( false );
  
  ll n; cin>>n;
  
  vc<double> p(n), q(n);
  rep(i,n){
    ll a; cin>>a;
    p[i]=a/1000.0;
  }
  rep(i,n){
    ll a; cin>>a;
    q[i]=a/100.0;
  }
  
  priority_queue<pair<double,int>> que;
  
  rep(i,n){
    que.emplace(p[i]*q[i], i);
  }
  
  double ans=0;
  rep(i,1001001){
    double now; int idx; tie(now, idx)=que.top(); que.pop();
    ans+=(i+1)*now;
    que.emplace(now*(1-q[idx]), idx);
  }
  printf("%.15lf\n", ans);
}