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

typedef long long ll;
typedef vector< int > vi;
typedef vector< vi > vvi;
typedef vector< ll > vl;
typedef vector< vl > vvl;
typedef pair< int, int > pii;
typedef vector< pii > vp;
typedef vector< double > vd;
typedef vector< vd > vvd;
typedef vector< string > vs;

template< class T1, class T2 >
int upmin( T1 &x, T2 v ){
  if( x > v ){
    x = v;
    return 1;
  }
  return 0;
}

template< class T1, class T2 >
int upmax( T1 &x, T2 v ){
  if( x < v ){
    x = v;
    return 1;
  }
  return 0;
}

const int INF = 0x3f3f3f3f;

int N;
vi P;
vi Q;

void init(){
  cin >> N;
  P = Q = vi( N );
  for( int i = 0; i < N; ++i )
    cin >> P[ i ];
  for( int i = 0; i < N; ++i )
    cin >> Q[ i ];
}

double ans;

void preprocess(){
  priority_queue< tuple< double, int > > pq;
  for( int i = 0; i < N; ++i )
    pq.emplace( P[ i ] / 1000. * Q[ i ] / 100., i );
  for( int i = 1; i <= 1000000; ++i ){
    double p; int id; tie( p, id ) = pq.top(); pq.pop();
    ans += p * i;
    pq.emplace( p * ( 1.0 - Q[ id ] / 100. ), id );
  }
}

void solve(){
  cout << fixed << setprecision( 5 ) << ans << endl;
}

signed main(){
  ios::sync_with_stdio( 0 );
  init();
  preprocess();
  solve();
  return 0;
}