import java.io.IOException;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws IOException {
		Scanner sn = new Scanner(System.in);
		
		int n = sn.nextInt();
		int len = String.valueOf(n).length();
		
		switch (len) {
		case 1:
			System.out.println(n);
			break;
		case 2:
			System.out.println(9);
			break;
		case 3:
			System.out.println(n - 90);
			break;
		case 4:
			System.out.println(900 + 9);
			break;
		case 5:
			System.out.println(n - (9000 + 90));
			break;
		case 6:
			System.out.println(90000 + 900 + 9);
			break;
		}
	}
	
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz