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

using namespace std;

typedef long long ll;

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;

	if (N < 1000000001ll) {
		printf("0\n");
	}
	else {
		int d = digit(N);
		if (d == 19) {
			d = 18;
			N = 999999999999999999ll;
		}
		for (i = 0; i <= 9; i++) {
			v[1].push_back(to_string(i));
		}
		v[2].push_back("00");
		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 = 0; 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);
				}
			}
		}

		ll ans = 0ll;

		for (k = 1; k <= d - 9; k++) {
			for (i = 0; i < v[k].size(); i++) {
				string s = v[k][i];
				for (j = 0; j < b[k]; j++) {
					s += to_string(0);
				}
				s += v[k][i];
				if (s[0] == '0') { continue; }
				if (stoll(s) <= N) {
					ans += 1ll;
				}
			}
		}
		printf("%lld\n", ans);
	}

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