#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  ll n;
  cin >> n;
  int ans = 0;
  for (int x = 1; x <= n; x++) {
    string s = to_string(x);
    string t = s + s + s;
    if (stoll(t) <= n)
      ans++;
    else
      break;
  }
  cout << ans << endl;
  return 0;
}