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

class Solution
{
    static double F(int n)
    {
        var m = Math.Sqrt(Enumerable.Range(1, n).Select(i => Math.Pow(0.81, i)).Sum());
        var d = Enumerable.Range(1, n).Select(i => Math.Pow(0.9, i)).Sum();
        return m / d;
    }

    static double F2(int n)
    {
        var max = 0.22941573;
        var m = F(n) - max;
        var d = F(1) - max;
        return m * 1200 / d;
    }

    static double G(double x)
    {
        return Math.Pow(2, x / 800);
    }

    static void Main()
    {
        var n = int.Parse(Console.ReadLine());
        var rperf = new int[n];
        for (int i = 0; i < n; i++)
        {
            rperf[i] = int.Parse(Console.ReadLine());
        }

        var m = Enumerable.Range(1, n).Select(i => G(rperf[i - 1]) * Math.Pow(0.9, i)).Sum();
        var d = Enumerable.Range(1, n).Select(i => Math.Pow(0.9, i)).Sum();
        var t = m / d;

        int x = 0;
        while (true)
        {
            if (t <= G(x))
            {
                break;
            }
            x++;
        }

        double result = x - F2(n);

        Console.WriteLine(Math.Round(result));
    }
}