#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <functional>
#include <cmath>
#include <complex>
#include <cctype>
#include <cassert>
#include <sstream>
#include <ctime>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

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

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;
typedef vector<ll> vl;
typedef vector<vl> vvl;

#define INF (1<<29)
#define INFL (1ll<<60)
#define EPS (1e-8)
#define PI (acos(-1))
const ll MOD = 1000000007ll;

string to_str(ll x) {
	stringstream ss;
	ss << x;
	return ss.str();
}

ll to_ll(string str) {
	stringstream ss(str);
	ll res;
	ss >> res;
	
	return res;
}

bool ispd(string str) {
	REP(i, str.size() / 2) if (str[i] != str[str.size() - 1 - i])
		return false;
	return true;
}

int main() {
	ll N;
	cin >> N;
	
	ll n = N / 1000000001;
	
	vector<ll> v;
	for (ll i = 1; i <= 100000; i++) {
		string now = to_str(i);
		
		string rev = now;
		reverse(ALL(rev));
		
		string tmp = now.substr(0, now.size() - 1) + rev;
		if (ispd(tmp) && tmp.size() < 10) v.push_back(to_ll(tmp));
		
		
		if (!ispd(now)) continue;
		
		tmp = now + rev;
		if (tmp.size() < 10) v.push_back(to_ll(tmp));
	}
	
	//cout <<"before:" <<  v.size() << endl;
	
	sort(ALL(v));
	v.erase(unique(ALL(v)), v.end());
	
	//cout <<"after: " <<  v.size() << endl;
	
	int ans = 0;
	REP(i, v.size()) {
		if (v[i] <= n) ans++;
	}
	cout << ans << endl;
	
	return 0;
}