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;//リストの使用
using System.Collections.Generic;
class Program
{
	static void Main()
	{
		long n = long.Parse(Console.ReadLine());
    long digit = whatDigit(n);
    long answer = 0;
    if(n<10) Console.WriteLine(n);
    else
    {
      answer += 9*(digit-1);
      long memo = 10;
      for(long i = 0; i < digit-2; i++)
      {
        memo *= 10;
      }
      answer += n / memo - 1;
      if(n % 10 == 9) answer++;
      Console.WriteLine(answer);
    }
	}
  
  static long whatDigit (long n)//nは何桁か
  {
    for(long i = 1; i < 20; i++)
    {
      n /= 10;
      if(n == 0)
      {
        return i;
        break;
      }
    }
    return 0;
  }
}