#include <bits/stdc++.h>
using namespace std;
int ROW[] = {+1, -1, +0, +0};
int COL[] = {+0, +0, +1, -1};
int X[] = {+0, +0, +1, -1, -1, +1, -1, +1};
int Y[] = {-1, +1, +0, +0, +1, +1, -1, -1};
int KX[] = {-2, -2, -1, -1, 1, 1, 2, 2};
int KY[] = {-1, 1, -2, 2, -2, 2, -1, 1};
long long GCD(long long a, long long b) { return b == 0 ? a : GCD(b, a % b); }
int LCM(int a, int b) { return a * (b / GCD(a, b)); }
bool CMP(int a, int b) { return a > b; }
int main() {
  long long n;
  cin >> n;
  long long ans = floor(log10(n));
  long long k = pow(10, ans);
  ans *= 9;
  k--;
  n -= k;
  while (n) {
    ans += n % 10;
    n /= 10;
  }
  cout << ans << endl;
  return 0;
}
