#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <sstream>
#include <climits>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <map>
#include <functional>
#include <set>
#include <numeric>
#include <stack>
#include <utility>
#include <time.h>
#include <iterator>
#include <bitset>
#include <random>
//#include "util.h"

using namespace std;
typedef unsigned uint;
typedef long long lint;
typedef unsigned long long ulint;



//呪文
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const pair<_KTy, _Ty>& m) { cout << "{" << m.first << ", " << m.second << "}"; return ostr; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const map<_KTy, _Ty>& m) { if (m.empty()) { cout << "{ }"; return ostr; } cout << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { cout << ", " << *itr; } cout << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const vector<_Ty>& v) { if (v.empty()) { cout << "{ }"; return ostr; }	cout << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { cout << ", " << *itr; }	cout << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const set<_Ty>& s) { if (s.empty()) { cout << "{ }"; return ostr; } cout << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { cout << ", " << *itr; }	cout << "}"; return ostr; }
//template <typename T> void print(T* v, int N) { if (N == 0) cout << "{ }"; cout << "{" << v[0]; for (int i = 1; i < N; i++) cout << ", " << v[i]; cout << "}"; }
#define PI 3.14159265358979323846
#define EPS 1e-8
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define all(x) (x).begin(), (x).end()



lint palindrome[200000];

int yuki0491()
{
	lint lo[10] = { 1, 1, 10, 10, 100, 100, 1000, 1000, 10000, 10000 };
	lint hi[10] = { 9, 9, 99, 99, 999, 999, 9999, 9999, 99999, 99999 };

	lint c = 1;
	for (lint i = 0; i < 10; i++) {
		for (lint j = lo[i]; j <= hi[i]; j++) {
			string S, T;
			S = T = to_string(j);
			if (i % 2 == 0) {
				T.pop_back();
			}
			while (!T.empty()) {
				S.push_back(T.back());
				T.pop_back();
			}
			palindrome[c] = stoll(S);
			c++;
		}
	}

	const lint X = 1000000001;
	lint N;
	cin >> N;
	
	lint K = N / X;

	c = 0;
	while (palindrome[c + 1] <= K) c++;

	cout << c << endl;

	return 0;
}

int main()
{
	//clock_t start, end;
	//start = clock();

	yuki0491();

	//end = clock();
	//printf("%d msec.\n", end - start);

	return 0;
}