#include <bits/stdc++.h>
using namespace std;
long long digitsum(long long int n) {
  long long int sum = 0;
  while (n > 0) {
    sum += n % 10;
    n /= 10;
  }
  return sum;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long a = 0, b = 0, n, count = 0, ans;
  cin >> n;
  long long int c = 0, k = n, r = 0;
  while (k > 0) {
    c++;
    k /= 10;
  }
  for (int i = 1; i < c; i++) r = r * 10 + 9;
  a = r;
  b = n - a;
  ans = digitsum(b) + 9 * (c - 1);
  cout << ans << endl;
  return 0;
}
