#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)
string wa[10] = { "0","1","2","3","4","5","6","7","8","9" };
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) {
			hogee.push(wa[i]);
		}
	}
	else {
		for (int i = 0;i < 10;++i) {
			hogee.push(wa[i]+wa[i]);
		}
	}
	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;
				for (int i = 0;i < judgement.size();++i) {
					if (n[i] > judgement[i]) {
						ans++;
						goto ok;
					}
					else if (n[i] < judgement[i]) goto ok;
				}
				ans++;
			ok:;
			}
		}
		else {
			for (int i = 0;i < 10;++i) {
				hogee.push(wa[i] + now + wa[i]);
			}
		}
	}
	cout << ans << endl;
	return 0;
}