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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.IO;

class Program
{
    static void Main(string[] args) {
        var writer = new StreamWriter(Console.OpenStandardOutput()) {AutoFlush = false};
        Console.SetOut(writer);
        Console.WriteLine(Solve());
        Console.Out.Flush();
    }
    static int Solve() {
        var N = Console.ReadLine();
        var len = N.Length;
        var result = N[0] - '0' + 9 * (len - 1);
        var isNines = true;
        for (int i = 1; i < len; i++) {
            if (N[i] == '9') continue;
            isNines = false;
            break;
        }
        return isNines ? result : result - 1;
    }
}