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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
using ll=long long;

int main(){
  ll n;
  cin >> n;
  int c=1;//桁数
  int k=1;//10^c
  
  int x=n;
  
  while(x>9){
    x/=10;
    k*=10;
    c++;
  }
  
  x=n/k;//nの1番左の数
  
  if(n+1==(x+1)*k) cout << x+9*(c-1) << endl;
  else cout << x+9*c-10 << endl;
}