using System;
using System.Collections.Generic;
using System.Text;
using sc = Scanner;
using System.Collections;
using System.Linq;


class Program
{
    static void Main(string[] args)
    {
        Solve();

#if DEBUG
        Console.WriteLine("終了するにはなにかキーを押して下さい...");
        Console.ReadKey();
#endif

    }

    static void Solve()
    {
        int n = sc.NextInt();
        int[] a = sc.NextIntArray();
        int sum = a.Sum();
        int size = 0;
        int range = 0;
        int answer = 0;
        for (int i = 1; i < 120; i++)//yoyuu wo mitumottoku
        {
            if (i*i > sum)
            {
                size = i - 1;
                range = 2 * size - 1;
                break;
            }
        }
        //size ga kisuu dearukoto wo riyousuru
        for (int i = 0; i < range/2; i++) //yobun na kazu wo kazoeage
        {
            if (i >= a.Length) break;
            answer += Math.Max(0, a[i] - (i + 1));
#if DEBUG
            Console.WriteLine(":::" + (i + 1));
            Console.WriteLine(i + ":" + answer);
#endif 
        }
        for (int i = range/2; i < range; i++)
        {
            if (i >= a.Length) break;
            answer += Math.Max(0,a[i] - (size + (range/2-i)));
#if DEBUG
            Console.WriteLine(":::" +(size+(range / 2 - i)));
            Console.WriteLine(i+":"+answer);
#endif 
        }

        Console.WriteLine(answer);
#if DEBUG
        Console.WriteLine("local check"); // Visual Studioのローカル変数チェック用
#endif 
    }


 }



public static class Scanner
{
    public static string[] NextStrArray()
    {
        return Console.ReadLine().Split(' ');
    }

    public static long[] NextLongArray()
    {
        string[] s = NextStrArray();
        long[] a = new long[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = long.Parse(s[i]);
        }
        return a;
    }
    public static int[] NextIntArray()
    {

        string[] s = NextStrArray();
        int[] a = new int[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = int.Parse(s[i]);
        }
        return a;
    }
    public static int NextInt()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return int.Parse(tmp);
    }
    public static double NextDouble()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return double.Parse(tmp);
    }
    public static long NextLong()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return long.Parse(tmp);
    }
    public static double[] NextDoubleArray()
    {

        string[] s = NextStrArray();
        double[] a = new double[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = double.Parse(s[i]);
        }
        return a;
    }
}