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;
using static System.Console;

class Program
{
    static void Main(string[] args)
    {
        var N = long.Parse(ReadLine());
        if (N<10)
        {
            WriteLine(N);
            return;
        }
        long max = CalcDigitSum(N);
        long tmp = 10;
        while (tmp <= N)
        {
            var val = CalcDigitSum(N - (N % tmp + 1));//n > m*10^p -1を満たす最大のm*10^p - 1の値
            if (val > max) max = val;
            tmp *= 10;
        }
        WriteLine(max);
    }
    static long CalcDigitSum(long num)
    {
        long res = 0;
        foreach (var item in num.ToString())
        {
            res += long.Parse(item.ToString());
        }
        return res;
    }
}