using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Diagnostics;
using System.Numerics;
using Enu = System.Linq.Enumerable;

class Program
{
    static readonly int TimeLimit = 1800;

    public void Solve()
    {
        var sw = Stopwatch.StartNew();
        int N = Reader.Int();
        var P = Reader.IntArray(N).Select(x => x / 1000.0).ToArray();
        var Q = Reader.IntArray(N).Select(x => x / 100.0).ToArray();
        var heap = new Heap<Tuple<double, int>>(true); // prob, index
        for (int i = 0; i < N; i++)
            heap.Push(Tuple.Create(P[i] * Q[i], i));
        double ans = 0;

        for (int count = 1; sw.ElapsedMilliseconds < TimeLimit; count++)
        {
            var t = heap.Pop();
            double prob = t.Item1;
            int i = t.Item2;
            ans += count * prob;
            heap.Push(Tuple.Create(prob * (1 - Q[i]), i));
        }

        Console.WriteLine(ans);
    }

    class Heap<T>
    {
        private const int InitialSize = 1024;
        private readonly int sign;
        private readonly Comparer<T> comp = Comparer<T>.Default;
        private T[] A = new T[InitialSize];
        public int Count { get; private set; }
        public Heap(bool greater = false) { sign = greater ? 1 : -1; }
        public T Peek() { return A[0]; }
        public bool Empty() { return Count == 0; }
        public void Push(T val)
        {
            if (Count == A.Length)
            {
                T[] next = new T[A.Length * 2];
                Array.Copy(A, next, A.Length);
                A = next;
            }
            A[Count++] = val;
            int i = Count - 1;
            while (i > 0)
            {
                int parent = (i - 1) / 2;
                if (Math.Sign(comp.Compare(val, A[parent])) == sign)
                {
                    A[i] = A[parent];
                    i = parent;
                }
                else break;
            }
            A[i] = val;
        }
        public T Pop()
        {
            T res = A[0];
            T val = A[--Count];
            if (Count == 0) return res;
            int i = 0;
            while (i * 2 + 1 < Count)
            {
                int L = i * 2 + 1;
                int R = i * 2 + 2;
                if (R < Count && Math.Sign(comp.Compare(A[R], A[L])) == sign) L = R;
                if (Math.Sign(comp.Compare(A[L], val)) == sign) { A[i] = A[L]; i = L; }
                else break;
            }
            A[i] = val;
            return res;
        }
    }
}


class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    private static TextReader reader = Console.In;
    private static readonly char[] separator = { ' ' };
    private static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    private static string[] A = new string[0];
    private static int i;
    private static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public static int[][] IntTable(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public static string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
    public static string Line() { return reader.ReadLine().Trim(); }
    private static string[] Split(string s) { return s.Split(separator, op); }
    private static string Next() { CheckNext(); return A[i++]; }
    private static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}