#include <bits/stdc++.h>
using namespace std;
#define int long long
#define Rep(i, N) for(int i = 0; i < N; i++)
#define AC 1000000001LL

signed main()
{
  int N;
  cin >> N;

  int ans = 0;
  for(int i = AC; i <= AC * AC; i = i * 10 + AC) {
    ans += min(9LL, N / i);
  }
  cout << ans << endl;

  return 0;
}