#include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

typedef long long ll;

ll a[15];
int b[10] = { 9,8,7,6,5,4,3,2,1,0 };
int digit(ll a);

vector<string>v[15];

int main() {

	ll N;

	scanf("%lld",&N);

	int i, j, k;

	a[1] = 9ll;
	a[2] = 9ll;

	for (i = 3; i < 12; i+=2) {
		a[i] = (a[i - 1] + 1ll) * 9ll;
		a[i + 1] = a[i];
	}

	if (N < 1000000001ll) {
		printf("0\n");
	}
	else {
		ll sum = 0ll;
		int d = digit(N);
		if (d == 19) {
			d = 18;
			N = 999999999999999999ll;
		}
		for (i = 10; i < d; i++) {
			sum += a[i - 9];
		}
		for (i = 1; i <= 9; i++) {
			v[1].push_back(to_string(i));
		}
		for (i = 11; i <= 99; i++) {
			if (i / 10 == i % 10) {
				v[2].push_back(to_string(i));
			}
		}
		for (i = 3; i <= 11; i++) {
			for (k = 1; k <= 9; k++) {
				string ss = to_string(k);
				for (j = 0; j < i - 2; j++) {
					ss += to_string(0);
				}
				ss += to_string(k);
				v[i].push_back(ss);
			}
			for (k = 1; k <= 9; k++) {
				for (j = 0; j < v[i - 2].size(); j++) {
					string s = to_string(k);
					s += v[i - 2][j];
					s += to_string(k);
					v[i].push_back(s);
				}
			}
		}
		for (i = 0; i < v[d - 9].size(); i++) {
			string s = v[d - 9][i];
			for (j = 0; j < b[d - 9]; j++) {
				s += to_string(0);
			}
			s += v[d - 9][i];
			if (stoll(s) <= N) {
				sum += 1ll;
			}
		}
		printf("%lld\n",sum);
	}

	return 0;
}
int digit(ll a) {
	int ret = 0;
	while (1) {
		if (a == 0ll) { break; }
		ret++;
		a /= 10ll;
	}
	return ret;
}