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# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args) {
        long n = long.Parse(Console.ReadLine());
        long l = digitLength(n);
        long f = digitFirst(n);
        Console.WriteLine((l-1)*9 + f);
    }
    static long digitLength(long x) {
        long length = 0;
        while(x>0) {
            length++;
            x /= 10;
        }
        return length;
    }
    static long digitFirst(long x) {
        long first = 0;
        List<long> digit = new List<long>();
        while(x>0) {
            first = x%10;
            digit.Add(x%10);
            x/=10;
        }
        for(int i = 0; i < digit.Count()-1; i ++) {
            if(i == digit.Count()-1)　continue;
            if(digit[i] != 9) {
                first -= 1L;
                break;
            }
        }
        
        return first;
    }
}