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.split("").map{|s| s.to_i}
ans = Array.new(getnum.size)

flg9 = 1

getnum.size.times do |keta|
    #最大桁以外が全て９の場合は処理しない
    if getnum[getnum.size - keta - 1] == 9 && flg9 == 1
        flg9 = 1
        ans[getnum.size - keta - 1] = getnum[getnum.size - keta - 1]
    else
        flg9 = 0
        if keta == getnum.size - 1
            ans[getnum.size - keta - 1] = getnum[getnum.size - keta - 1] - 1
        else
            ans[getnum.size - keta - 1] = 9
        end
    end
end

puts ans.inject(:+)