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: Wrong Answer)

getnum = gets.chomp
number = getnum.to_i
num = getnum.split("").map{|x| x.to_i}

a_new_num = Array.new(num.size)
new_num = ""
flg = 0
flg9 = 1

num.size.times do |keta|
    if flg == 0
        if keta == 0 && num[num.size - 1 - keta] == 9
            a_new_num[num.size - 1 - keta] = 0
            flg = 0
        else
            a_new_num[num.size - 1 - keta] = num[num.size - 1 - keta] + 1 
            flg = 1
        end
    else
        a_new_num[num.size - 1 - keta] = num[num.size - 1 - keta]
        flg = 1
    end
    
    if num[num.size - 1 - keta] == 9 && flg9 == 1
        flg9 = 1
    else
        flg9 = 0
    end
end

a_new_num[0] = 0
   
num.size.times do |keta|
    new_num << a_new_num[keta].to_s
end

if flg9 == 1
    new_num = "0"
end

ans = (number - new_num.to_i).to_s.split("").map{|x| x.to_i}
puts ans.inject(:+)