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 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <math.h>
int main()
{   long long n;
    scanf("%lld",&n);
    long long cpy=n;
    int sum=0;
    int dig=0;
    while(cpy>0){
        sum+=cpy%10;
        cpy/=10;
        dig++;
    }
    int head=n/pow(10,(dig-1));
    if((sum-head)==9*(dig-1)){
        printf("%d",(dig-1)*9+head);
    }else{
        printf("%d",(dig-1)*9+head-1);
    }
    return 0;
}