#include <string>
#include <iostream>
#include <algorithm>
using namespace std;
int solve(int x) {
	int ret = 0;
	for (int i = 1; i <= 9; i++) {
		if (i <= x) ret++;
	}
	for (int i = 1; i < 10000; i++) {
		string t1 = to_string(i), t2 = t1;
		reverse(t1.begin(), t1.end());
		if (stoi(t1 + t2) <= x) ret++;
		for (int j = 0; j <= 9; j++) {
			if (stoi(t1 + to_string(j) + t2) <= x) ret++;
		}
	}
	return ret;
}
long long n;
int main() {
	cin >> n;
	int x = 1000000000;
	int p = n / x, q = n % x;
	cout << solve(p - 1) + (q >= p) << endl;
	return 0;
}