#include <bits/stdc++.h>
using namespace std;
const long long inf = 0x3f3f3f3f;
const int N = 2e6;
const long long mod = 998244353;
map<string, long long> mp;
map<string, int> ml;
long long n, m, k, b[N], f[N], c[N], a[N], d;
int did[N], vis[N], num[N];
string s, ss;
long long s1, s2, s3, s4 = 0, flag, tot, t, sum, pos, cnt, x, y, xx, yy, ans,
                      dex1, dex2;
vector<long long> v;
set<int> second;
long long dp[200][200];
long long fenjie(long long xx) {
  long long ssum = 0;
  while (xx) {
    ssum = ssum + xx % 10;
    xx /= 10;
  }
  return ssum;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n;
  x = n;
  while (x >= 10) {
    cnt++;
    x /= 10;
  }
  t = 1;
  for (int i = 1; i <= cnt; i++) t *= 10;
  t--;
  sum += (cnt)*9 + fenjie(n - t);
  cout << sum << endl;
}
