#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const int mod2 = 1e9 + 9;
const int maxN = 2e3;
const int INF = 1e9 + 7;
const int maxedge = 1e6 + 100;
const long long LL_INF = 1e18 + 11;
using namespace std;
long long ans, n, x, cnt;
void file() {
  freopen("cubes.in", "r", stdin);
  freopen("cubes.out", "w", stdout);
}
void boost() {
  ios_base ::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
}
int main() {
  cin >> n;
  while (true) {
    if ((cnt * 10) + 9 > n) {
      break;
    } else {
      cnt = (cnt * 10) + 9;
      ans += 9;
    }
  }
  x = n - cnt;
  while (x > 0) {
    ans += (x % 10);
    x /= 10;
  }
  cout << ans;
}
