#include <bits/stdc++.h>
using namespace std;
long long power(long long x, long long y) {
  long long res = 1;
  while (y > 0) {
    if (y & 1) res = (res * x);
    y = y >> 1;
    x = (x * x);
  }
  return res;
}
long long summ(long long a) {
  long long ans = 0;
  while (a) {
    ans += a % 10;
    a = a / 10;
  }
  return ans;
}
long long digit(int n) {
  int count = 0;
  while (n) {
    n = n / 10;
    count++;
  }
  return count;
}
long long sum(long long a) {
  long long ans = 0;
  while (a) {
    ans += (a % 10);
    a = a / 10;
  }
  return ans;
}
int main() {
  long long n;
  cin >> n;
  long long a = n;
  long long b;
  long long count = 0;
  while (a) {
    b = a % 10;
    a = a / 10;
    count++;
  }
  count--;
  b--;
  b = b * pow(10, count);
  long long c = 0;
  for (int i = 0; i < count; i++) {
    c = (10 * c) + 9;
  }
  b = b + c;
  c = n - b;
  cout << sum(b) + sum(c);
  return 0;
}
