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: Wrong Answer)

using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        char[] input = Console.ReadLine().ToCharArray();
        int[] n = Array.ConvertAll(input, i => (int)Char.GetNumericValue(i));

        if (n.Length <= 2)
        {
            Console.WriteLine(n.Sum());
            return;
        }
        int lastIndex = n.Length - 1;
        for (int i = 2; i < lastIndex - 1; i++)
        {
            n[i] = 9;
        }

        if (n[0] + n[1] < n[0] - 1 + 9)
        {
            n[0]--;
            n[1] = 9;
            if (lastIndex - 1 != 1)
            {
                if (n[lastIndex - 1] + n[lastIndex] < 9 + 9)
                {
                    n[lastIndex - 1] = 9;
                    n[lastIndex] = 9;
                }
            }
            else
                n[lastIndex] = 9;
        }
        else
        {
            if (n[lastIndex - 1] + n[lastIndex] < n[lastIndex - 1] - 1 + 9)
            {
                n[lastIndex - 1]--;
                n[lastIndex] = 9;
            }
        }
        Console.WriteLine(n.Sum());
    }
}