import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        Room[] rooms = new Room[n];
        for (int i = 0; i < n; i++) {
            rooms[i] = new Room(sc.nextInt());
        }
        for (int i = 0; i < n; i++) {
            rooms[i].find(sc.nextInt());
        }
        PriorityQueue<Room> queue = new PriorityQueue<>();
        for (int i = 0; i < n; i++) {
            queue.add(rooms[i]);
        }
        double ans = 0;
        for (int i = 1; i < 1000000; i++) {
            Room r = queue.poll();
            ans += r.rate * i;
            r.add();
            queue.add(r);
            //System.out.println(ans);
        }
        System.out.println(ans);
    }
    
    static class Room implements Comparable<Room> {
        double lostRate;
        double findRate;
        double notFindRate;
        double rate;
        
        public Room(int x) {
            lostRate = x / 1000.0;
        }
        
        public void find(int x) {
            findRate = x / 100.0;
            notFindRate = 1 - findRate;
            rate = lostRate * findRate;
        }
        
        public void add() {
            rate *= notFindRate;
        }
        
        public int compareTo(Room another) {
            if (rate == another.rate) {
                return 0;
            } else if (rate < another.rate) {
                return 1;
            } else {
                return -1;
            }
        }
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String nextLine() throws Exception {
        return br.readLine();
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}