using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var N = int.Parse(Console.ReadLine());
        var A = Console.ReadLine().Split().Select(double.Parse).ToArray();
        var p = 1D;
        foreach (var item in A)
        {
            p *= (1000 - item) / 1000;
        }
        Console.WriteLine(1000 * (1 - p));
    }
}