import java.util.Scanner;

public class Main {

    static long solve(long n) {
        if (n <= 9) return n;
        char[] s = String.valueOf(n).toCharArray();
        long res = 0L;
        int len = s.length;
        for (int i = len - 1; i > 0; i--) {
            res += 9;
            if (s[i] < '9') {
                s[i - 1] = (char) (s[i - 1] - 1);
            }
        }
        res += s[0] - '0';
        return res;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long n = in.nextLong();
        System.out.println(solve(n));
    }

}