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

string to_str(int n) {
  ostringstream os;
  os << n;
  return os.str();
}

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

  int ans = 0;
  Reps(i, 1, 100000) {
    string T = to_str(i), R = T;
    string S, F;
    reverse(R.begin(), R.end());
    
    if(i < 10000) {
      S = T + R;
      int ssize = (int)S.size();
      Rep(j, 9 - ssize) S += '0';
      S += T + R;
    } else S = "1000000000000000001";
    
    T = to_str(i / 10);
    F = T + R;
    int fsize = (int)F.size();
    Rep(j, 9 - fsize) F += '0';
    F += T + R;
    //cout << S << " " << F << endl;
    int A, B;
    sscanf(S.c_str(), "%lld", &A);
    sscanf(F.c_str(), "%lld", &B);
    //cout << A << " " << B << endl;
    if(N >= A) ans++;
    if(N >= B) ans++;
  }

  cout << ans << endl;
    
  return 0;
}