import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		new Main().run();
	}

	static long N;
	static long FACTOR = 1_000_000_000 + 1;
	static long[] pow10 = new long[19];

	void run() {
		pow10[0] = 1;
		for (int i = 1; i < pow10.length; ++i)
			pow10[i] = pow10[i - 1] * 10;

		Scanner sc = new Scanner(System.in);
		N = sc.nextLong();
		if (N < FACTOR) {
			System.out.println(0);
			return;
		}
		long ans = 0;
		for (long v = 1; v < pow10[6]; ++v) {
			long d = 0;
			int s = 0;
			int t = 2 * String.valueOf(v).length() - 1;
			while (t - s > 0) {
				long digi = (v % pow10[s + 1] / pow10[s]);
				d += digi * (pow10[s] + pow10[t]);
				++s;
				--t;
			}
			if (d >= pow10[9])
				continue;
			d *= FACTOR;
			if (d <= N) {
				++ans;
			}
		}

		for (int i = 1; i <= 9; ++i) {
			if (i * FACTOR <= N)
				++ans;
		}
		System.out.println(ans);
	}

	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}