import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class _491 {
	public static void main(String[] args) throws IOException {
		new _491().solve();
	}

	void solve() throws IOException {
		try (final Scanner in = new Scanner(System.in)) {
			n = in.nextLong();
			long ans = 0;
			for (int i = 1; i <= 9; i++) {
				ans += rec(i, 0, 0);
			}
			System.out.println(ans);
		}
	}
	
	long n;
	char[] cs;
	long x = 1000000000+1;
	long rec(int len, int idx, long cur) {
		if (len % 2 == 0) {
			if (2*idx == len) {
				long c = cur;
				for (int i = 0; i < len / 2; i++) {
					cur = cur * 10 + c % 10;
					c /= 10;
				}
//				if (cur * x <= n) dump(cur);
				return cur * x <= n ? 1 : 0;
			}
		} else {
			if (2*idx-1 == len) {
				long c = cur;
				for (int i = 0; i < len / 2; i++) {
					cur = cur * 10 + c % 10;
					c /= 10;
				}
//				if (cur * x <= n) dump(cur);
				return cur * x <= n ? 1 : 0;
			}
		}
		
		long ans = 0;
		for (int i = 0; i < 10; i++) {
			if (cur == 0 && i == 0) continue;
			ans += rec(len, idx + 1, cur * 10 + i);
		}
		return ans;
	}
	
	// for debug
	static void dump(Object... o) {
		System.err.println(Arrays.deepToString(o));
	}
}