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,N0,i,sum=0,sum_max=0,a,count=0;

    scanf("%lld",&N);
    if(N<10){
        printf("%lld",N);
        return 0;
    }
    N0=N;
    while(N>=10){
        sum += 9;
        N = N/10;
        a = N%10;
        count++;
    }
    if(N0 == (a+1)*pow(10,count)-1){
        printf("%lld\n",sum+a);
    }else{
        printf("%lld\n",sum+a-1);
    }
    return 0;
}