#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <iomanip>
#include <time.h>
#include <random>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(long long i = 0;i < n;++i)
int judge(string a, string b) {
	for (int i = 0;i < a.size();++i) {
		if (a[i] < b[i]) return true;
		else if (a[i] > b[i]) return false;
	}
	return true;
}
int main() {
	string n;
	cin >> n;
	if (n.length() <= 9) {
		cout << 0 << endl;
		return 0;
	}
	long long ans = 0;
	long long pointer = 1;
	for (int i = 0;i < n.length() - 10;++i) {
		if (i % 2 == 0) pointer *= 9;
		ans += pointer;
	}
	//計算が必要な部分
	queue<string> hogee;
	int cnt = n.length() - 9;
	if (cnt % 2 == 1) {
		for (int i = 0;i < 10;++i) {
			string hoge;
			hoge.push_back(i + '0');
			hogee.push(hoge);
		}
	}
	else {
		for (int i = 0;i < 10;++i) {
			string hoge;
			hoge.push_back(i + '0');
			hoge.push_back(i + '0');
			hogee.push(hoge);
		}
	}
	while (hogee.empty() == false) {
		string now = hogee.front();
		hogee.pop();
		if (now.size() == cnt) {
			if (now[0] != '0') {
				string judgement = now;
				for (int i = 0;i < 9 - now.size();++i) {
					judgement.push_back('0');
				}
				judgement += now;
				if (judge(judgement,n)) {
					ans++;
				}
			}
		}
		else {
			for (int i = 0;i < 10;++i) {
				string a,b;
				a.push_back(i + '0');
				b.push_back(i + '0');
				hogee.push(a + now + b);
			}
		}
	}
	cout << ans << endl;
	return 0;
}