using System;
using System.Linq;

public class MyClass
{
    public static void Main()
    {
        int N = int.Parse(Console.ReadLine());
        var array = Array.ConvertAll<string, int>(Console.ReadLine().Split(new char[]{' '}, StringSplitOptions.RemoveEmptyEntries), int.Parse);
        int res = int.MaxValue;
        for (int i = 1; i <= 1111; i+=2)
        {
            res = Math.Min(res, Count(i, array));
        }
        Console.WriteLine(res);
    }

    private static int Count(int end, int[] array)
    {
        int sum = array.Sum();
        int tmp = end / 2 + 1;
        if (sum < tmp * tmp)
        {
            return int.MaxValue;
        }
        int res = sum;
        for (int i = 0; i < end; i++)
        {
            res -= Math.Min((i >= array.Length ? 0 : array[i]), Math.Min(i + 1, end - i));
        }//for i
        return res;
    }

}