using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CityQuarter
{
    class Program
    {
        static void Main(string[] args)
        {
            int r = int.Parse(Console.ReadLine());
            int counter = 0;
            for (int x = -r; x <0; x++)
                counter += (int)Math.Ceiling(Math.Sqrt(r * r - (x + 1) * (x + 1)));
            Console.WriteLine(counter * 4);
        }
    }
}