#include <bits/stdc++.h>
using namespace std;
int sum(long long n) {
  int res = 0;
  while (n > 0) {
    res += n % 10;
    n /= 10;
  }
  return res;
}
int solve_slow(long long n) {
  int res = 0;
  for (long long a = 0, b = n; a <= b; a++, b--) {
    res = max(res, sum(a) + sum(b));
  }
  return res;
}
int solve_fast(long long n) {
  if (n <= 10) return (int)n;
  long long x = 9;
  while (x * 10 + 9 <= n) {
    x = x * 10 + 9;
  }
  auto other = n - x;
  return sum(x) + sum(other);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  long long n;
  cin >> n;
  cout << solve_fast(n) << endl;
}
