#include <iostream>
#include <cstdio>
#include <algorithm>
#include <functional>
#include <string>
#include <vector>
#include <set>
#include <map>

using namespace std;

vector<unsigned long long> a;

unsigned long long stoiii(string s) {
	unsigned long long val = 0;
	for (char c : s) {
		val = val * 10 + (c - '0');
	}
	return val;
}

void dfs(string curr) {
	if (!curr.empty() && curr[0] != '0') {
		a.push_back(stoiii(curr));
	}
	if (curr.size() >= 9) {
		return;
	}
	for (int i = 0; i < 10; i++) {
		string c(1, i + '0');
		dfs(c + curr + c);
	}
}

int main() {
	long long n;
	cin >> n;
	dfs("");
	for (int i = 0; i < 10; i++) {
		dfs(string(1, '0' + i));
	}
	int ans = 0;
	for (unsigned long long x : a) {
		unsigned long long y = 1000000000 * x + x;
		if (y <= n) {
			ans++;
		}
	}
	cout << ans << endl;
}