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 System.Text;
using System.Threading.Tasks;

namespace Contest
{
    class Scanner
    {
        private string[] line = new string[0];
        private int index = 0;
        public string Next()
        {
            if (line.Length <= index)
            {
                line = Console.ReadLine().Split(' ');
                index = 0;
            }
            var res = line[index];
            index++;
            return res;
        }
        public int NextInt()
        {
            return int.Parse(Next());
        }
        public long NextLong()
        {
            return long.Parse(Next());
        }
        public string[] Array()
        {
            line = Console.ReadLine().Split(' ');
            index = line.Length;
            return line;
        }
        public int[] IntArray()
        {
            return Array().Select(int.Parse).ToArray();
        }
        public long[] LongArray()
        {
            return Array().Select(long.Parse).ToArray();
        }
    }

    class Program
    {
        private string N;
        private void Scan()
        {
            var sc = new Scanner();
            N = sc.Next();
        }

        public void Solve()
        {
            Scan();
            var dp = new int[N.Length + 1];
            var dp2 = new int[N.Length + 1];
            dp2[0] = 0;
            var NN = long.Parse(N);
            for (int i = 1; i <= N.Length; i++)
            {
                dp2[i] = dp2[i - 1] + (int)(NN % 10);
                if (NN % 10 != 0)
                {
                    dp2[i] = Math.Max(dp2[i], 9 * (i - 1) + (int)(NN % 10 - 1));
                }
                NN /= 10;
            }
            Console.WriteLine(dp2[N.Length]);
        }

        static void Main(string[] args)
        {
            new Program().Solve();
        }
    }
}