#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const long long MAX = 5100000;
const long long INF = 1LL << 60;
const long long mod = 1000000007LL;
//const long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;


int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/
	ll m = mod + 2;
	ll n; cin >> n;
	ll tm = n / m;
	ll res = 0;
	for (ll i = 1; i <= 9; i++) {
		if (m * i <= n) res++;
	}
	for (ll i = 1; i <= tm; i++) {
		string s = to_string(i);
		string t = s;
		reverse(t.begin(), t.end());
		s += t;
		t = s;
		ll sz = s.size();
		for (ll i = sz; i < 9; i++) {
			s += '0';
		}
		s += t;
		if (stoll(s) > n) break;
		res++;
	}
	cout << res << endl;
	return 0;
}