Problem:
Score : 300 points

Problem Statement

Find the maximum possible sum of the digits (in base 10) of a positive integer not greater than N.

Constraints

1\leq N \leq 10^{16}

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the maximum possible sum of the digits (in base 10) of a positive integer not greater than N.

Sample Input 1

100

Sample Output 1

18

For example, the sum of the digits in 99 is 18, which turns out to be the maximum value.

Sample Input 2

9995

Sample Output 2

35

For example, the sum of the digits in 9989 is 35, which turns out to be the maximum value.

Sample Input 3

3141592653589793

Sample Output 3

137

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

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

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var value  = Console.ReadLine();
            var digit = value.Length;


            if (!(value.StartsWith("9")))
            {
                if (digit == 1)
                {
                    Console.WriteLine(value);
                    return;
                }

                var number9 = Get9Number(value);
                Console.WriteLine(number9 - GetSisu(digit));
            }

            var errorDigit = GetResult(value);
            Console.WriteLine(Get9Number(value) - GetSisu(errorDigit + 1));
        }

        static int GetSisu(int digit)
        {
            return (int)(Math.Pow(10,digit - 1));
        }

        static int Get9Number(string value)
        {
            List<string> charList = new List<string>();
            charList.Add(value.Substring(0, 1));
            charList.AddRange(Enumerable.Repeat("9", value.Length - 1).ToList());
            return int.Parse(string.Join("", charList));
        }

        static int GetResult(string value)
        {
            if (!(value.StartsWith("9"))) {
                return value.Length;
            } else {
                return GetResult(value.Substring(1, value.Length - 1));
            }
        }


    }
}