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"
)

const mod = 1000000007

// 1MB
const ioBufferSize = 1 * 1024 * 1024

var sc = func() *bufio.Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Buffer(make([]byte, ioBufferSize), ioBufferSize)
	sc.Split(bufio.ScanWords)
	return sc
}()

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

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func main() {
	n := nextInt()

	f, d := 0, 0
	for m := n; m > 0; m /= 10 {
		f = m
		d++
	}

	md := f
	for i := 1; i < d; i++ {
		md *= 10
		md += 9
	}

	if n == md {
		fmt.Println(f + (d-1)*9)
	} else {
		fmt.Println(f - 1 + (d-1)*9)
	}
}