using System;

public class Hello
{
    static void Main()
    {
        Console.ReadLine();
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, int.Parse);
        getAns(a);
    }
    static void getAns(int[] a)
    {
        var b = 1d;
        foreach (var x in a) b *= (1000d - x) / 1000d;
        Console.WriteLine(1000d - 1000d * b);
    }
}