#include <bits/stdc++.h>
using namespace std;
long long int n, a, b;
long long int S(long long int x) {
  int ret = 0;
  long long int y = n - x;
  while (x > 0) {
    ret += x % 10;
    x /= 10;
  }
  while (y > 0) {
    ret += y % 10;
    y /= 10;
  }
  return ret;
}
long long int solve(long long int x) {
  long long int b = 1, ans = x;
  while (x) {
    long long int cur = (x - 1) * b + (b - 1);
    if (S(cur) > S(ans)) {
      ans = cur;
    }
    x /= 10;
    b *= 10;
  }
  return ans;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  cout << S(solve(n));
  return 0;
}
