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 ds n
  res = 0
  while n>0
    res += n%10
    n /= 10
  end
  res
end

n = gets.to_i
ans = [ds(n)]
n = n.to_s

t = 0
while n.size!=0
  t += n[0].to_i
  ans << t-1+ds(10**(n.size-1)-1)
  n = n[1..-1]
end

p ans.max