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: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;

namespace Algorithm
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = long.Parse(Console.ReadLine());
            var S = N.ToString();

            var allNine = true;
            for (var i = 1; i < S.Length; i++)
            {
                if (S[i] != '9')
                {
                    allNine = false;
                    break;
                }
            }

            var val = 0;
            if (allNine)
                foreach (var c in S) val += int.Parse(c.ToString());
            else
            {
                N -= (long)Math.Pow(10, S.Length - 1);
                val = N.ToString()[0] == '0' || N.ToString().Length == 1 ? 0 : int.Parse(N.ToString()[0].ToString());
                var remin = new string('9', S.Length - 1);

                foreach (var r in remin) val += int.Parse(r.ToString());
            }

            Console.WriteLine($"{val}");
        }
    }
}