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

namespace PageNumbers
{
    class Program
    {
        static void Main(string[] args)
        {
            int digits = int.Parse(Console.ReadLine());
            int sumOfDigits = 0;
            int currentPage = 0;

            while (true)
            {
                if (currentPage <= 9)
                {
                    sumOfDigits++;
                }
                else if(currentPage >=10 && currentPage <= 99)
                {
                    sumOfDigits += 2;
                }
                else if (currentPage >= 100 && currentPage <= 999)
                {
                    sumOfDigits += 3;
                }
                else if (currentPage >= 1000 && currentPage <= 9999)
                {
                    sumOfDigits += 4;
                }
                else if (currentPage >= 10000 && currentPage <= 99999)
                {
                    sumOfDigits += 5;
                }
                else if (currentPage >= 100000 && currentPage <= 999999)
                {
                    sumOfDigits += 6;
                }

                currentPage++;

                if (sumOfDigits >= digits)
                {
                    break;
                }
            }

            Console.WriteLine(currentPage-1);
        }
    }
}