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 Lua (5.3.2) (judge verdict: Accepted)

local s = io.read()
local all9 = true
for i = 2, #s do
  if s:sub(i, i) ~= "9" then
    all9 = false
  end
end
local n = tonumber(s:sub(1, 1))
n = n + 9 * (#s - 1)
if not all9 then n = n - 1 end
print(n)