using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Globalization;
using System.Diagnostics;
using static System.Console;
using Pair = System.Collections.Generic.KeyValuePair<int, int>;
//using System.Numerics;

class Program
{
    static void Main()
    {
        //SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        new Program().solve();
        Out.Flush();
    }
    Scanner cin = new Scanner();
    Random rnd = new Random();
    Stopwatch sw = new Stopwatch();
    readonly int[] dd = { 0, 1, 0, -1, 0 };
    readonly int mod = 1000000007;
    readonly string alfa = "abcdefghijklmnopqrstuvwxyz";
    readonly string ALFA = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    int N;
    int[] R;
    void solve()
    {
        N = cin.nextint;
        R = new int[N];
        for (int i = 0; i < N; i++)
        {
            R[i] = cin.nextint;
        }
        WriteLine(ratingN().ToString("F0"));
    }
    double ratingN()
    {
        var L = R.Select(i => g(i)).ToArray();
        var E = Enumerable.Range(1, N).Select(i => Math.Pow(0.9, i)).ToArray();
        for (int i = 0; i < N; i++)
        {
            L[i] *= E[i];
        }
        //WriteLine(1 / g(L.Sum() / E.Sum()));
        return arcg(L.Sum() / E.Sum()) - f();

    }
    double g(double X)
    {
        //WriteLine("g " + Math.Pow(2.0, X / 800));
        return Math.Pow(2.0, X / 800);
    }
    double f()
    {
        return (F(N) - F(1000000)) / (F(1) - F(1000000)) * 1200;
    }
    double F(int n)
    {
        var E1 = Enumerable.Range(1, n).Select(i => Math.Pow(0.81, i));
        var E2 = Enumerable.Range(1, n).Select(i => Math.Pow(0.9, i));
        return Math.Sqrt(E1.Sum()) / E2.Sum();
    }
    double arcg(double Y)
    {
        return 800 * Math.Log(Y) / Math.Log(2);
    }

}

class Scanner
{
    string[] s; int i;
    char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] scan { get { return ReadLine().Split(); } }
    public int[] scanint { get { return Array.ConvertAll(scan, int.Parse); } }
    public long[] scanlong { get { return Array.ConvertAll(scan, long.Parse); } }
    public double[] scandouble { get { return Array.ConvertAll(scan, double.Parse); } }
    public string next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return next;
        }
    }
    public int nextint { get { return int.Parse(next); } }
    public long nextlong { get { return long.Parse(next); } }
    public double nextdouble { get { return double.Parse(next); } }
}