#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  int m = 0;
  while (n > 9) {
    n -= 9;
    m += 9 + n % 10;
    n /= 10;
  }
  cout << m + n << endl;
  return 0;
}
