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.Linq;
using System.Text;

class Program
{
	static void Main()
	{
		var s = Console.ReadLine();
		if (s.Length == 1) {
			Console.WriteLine(int.Parse(s));
		} else {
			var builder = new StringBuilder();
			for (var i = 0; i < s.Length - 1; ++i) {
				builder.Append("9");
			}

			var answer = int.Parse(s.First().ToString());
			if (builder.ToString() != s.Substring(1)) {
				--answer;
			}

			answer += 9 * (s.Length - 1);
			Console.WriteLine(answer);
		}
	}
}