package main

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

func main() {
	in := bufio.NewReader(os.Stdin)
	var s string
	fmt.Fscan(in, &s)

	digits := make([]int, 0, len(s))
	for i := len(s) - 1; i >= 0; i-- {
		digits = append(digits, int(s[i]-'0'))
	}

	const neg = -1 << 30
	dp := [2]int{0, neg}

	for _, d := range digits {
		ndp := [2]int{neg, neg}
		for carryIn := 0; carryIn <= 1; carryIn++ {
			if dp[carryIn] == neg {
				continue
			}
			for carryOut := 0; carryOut <= 1; carryOut++ {
				sumDigits := d - carryIn + 10*carryOut
				if 0 <= sumDigits && sumDigits <= 18 {
					val := dp[carryIn] + sumDigits
					if val > ndp[carryOut] {
						ndp[carryOut] = val
					}
				}
			}
		}
		dp = ndp
	}

	fmt.Println(dp[0])
}