import java.util.*;
import java.lang.*;
import java.io.*;

class Main {
	public static void main (String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int m = 1;
		while (true) {
			if (m < 10) {	//1 digit
				n -= 1;
			} else if (m < 100) {	//2 digits
				n -= 2;
			} else if (m < 1000) {	//3 digits
				n -= 3;
			} else {	//4 digits
				n -= 4;
			}
			if (n < 0) {
				m = 0;
			}
			if (n <= 0) {
				break;
			}
			m++;
		}
		System.out.print(m);
	}
}