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 (2.7.1) (judge verdict: Wrong Answer)

a = gets.split('').map(&:to_i).reverse
b = []
i=0
while i < a.length
  if a[i]== -1
    a[i] = 9
    a[i+1]-=1
  end
  if a[i] != 9
    if i+1 == a.length
      b << a[i]
    else
      b << 9
      a[i+1]-=1
    end
  else
    b << 9
  end
  i+=1
end
puts b.sum