```go
package main

import (
	"fmt"
)

func f(x int) int {
	x += 1
	for x%10 == 0 {
		x /= 10
	}
	return x
}

func main() {
	var n int
	fmt.Scan(&n)

	visited := make(map[int]bool)
	visited[n] = true

	for {
		n = f(n)
		if visited[n] {
			break
		}
		visited[n] = true
	}

	fmt.Println(len(visited))
}
```