#include <bits/stdc++.h>
using namespace std;
long long int sum(long long int n) {
  long long int s2um = 0;
  while (n > 0) {
    s2um += n % 10;
    n = n / 10;
  }
  return s2um;
}
long long int answer(long long int n) {
  long long int x = 0, y = 0;
  while (10 * y + 9 < n) {
    y = 10 * y + 9;
    x = x + 9;
  }
  long long int m = n - y;
  x += sum(m);
  return x;
}
int main() {
  ios_base::sync_with_stdio(false);
  std::cin.tie(NULL);
  std::cout.tie(NULL);
  long long int n;
  cin >> n;
  cout << answer(n);
  return 0;
}
