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 Ruby (2.3.3) (judge verdict: Accepted)

def search(n, m, i)
  return 0 if i == m

  y = 9 * ((m - 1) - i)

  if n[i] == 0 then
    return y
  end

  return [
    n[i] + search(n, m, i + 1),
    (n[i] - 1) + y
  ].max
end

def main(argv)
  n = gets.chomp.split('').map{|c| c.ord - '0'.ord}
  m = n.size

  puts search(n, m, 0).to_s
end

if self.to_s == 'main' then
  main(ARGV)
end