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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func init() {
	const maxWord = (1 << 30)
	buf := []byte{}
	sc.Buffer(buf, maxWord)
	sc.Split(bufio.ScanWords)
}

func input() string {
	sc.Scan()
	return sc.Text()
}

func splitDigit(n int) []int {
	digit := make([]int, 0, 20)
	for n > 0 {
		digit = append(digit, n%10)
		n /= 10
	}
	return digit
}

func solve(n int) int {
	digit := splitDigit(n)
	k := len(digit)
	c := digit[k-1]
	for i := 0; i < k-1; i++ {
		if digit[i] != 9 {
			return c + 9*(k-1) - 1
		}
	}

	return c + 9*(k-1)
}

func main() {
	n, _ := strconv.Atoi(input())
	fmt.Println(solve(n))
}