#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;
}

int main() {
	ll N;
	cin >> N;
	
	ll n = N / 1000000001;
	
	int ans = 0;
	
	for (ll i = 1; i < 100500; i++) {
		string now = to_str(i);
		
		string rev = now;
		reverse(ALL(rev));
		
		if (now.size() % 2 == 1) {
			bool ok = true;
			REP(i, now.size() / 2) if (now[i] != now[now.size() - 1])
				ok = false;
			if (ok) {
				ll num = to_ll(now) * 1000000001;
				if (num <= N) ans++;
			}
		}
		
		if (now != rev) continue;
		
		ll num = to_ll(now + rev) * 1000000001;
		if (num <= N) ans++;
	}
	
	cout << ans << endl;
	
	return 0;
}