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 Scala (2.13.1) (judge verdict: Accepted)

object Main extends App {
  @scala.annotation.tailrec
  def loop(chars: Seq[Char], acc: Seq[Char]): Int = chars match {
    case Seq() => acc.map(i => new String(Array(i)).toInt).sum
    case x :: xs if x == '9' => loop(xs, acc :+ x)
    case xs => xs.length * 9 + acc.map(i => new String(Array(i)).toInt).sum - 1
  }
  val sc = new java.util.Scanner(System.in)
  val x :: xs = sc.next().toCharArray.toList
  println(if (xs.isEmpty) x.toString else loop(xs, Seq(x)))
}