#include <bits/stdc++.h>
long long p[16];
void F() {
  p[1] = 10;
  for (int i = 2; i <= 14; i++) p[i] = p[i - 1] * 10;
}
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  F();
  long long n, ans = 0;
  cin >> n;
  if (n < 10) {
    cout << n;
    return 0;
  }
  for (int i = 1; i <= 14; i++) {
    if (n / p[i] == 0) {
      long long a = p[i - 1] - 1;
      long long b = n - a;
      ostringstream str1, str2;
      str1 << a;
      str2 << b;
      string sa = str1.str();
      string sb = str2.str();
      for (auto x : sa) ans += x - '0';
      for (auto x : sb) ans += x - '0';
      cout << ans;
      return 0;
    }
  }
  return 0;
}
