Problem:
Score : 200 points

Problem Statement

Given is an integer N. Find the number of positive integers less than or equal to N that have an odd number of digits (in base ten without leading zeros).

Constraints

1 \leq N \leq 10^5

Input

Input is given from Standard Input in the following format:

N

Output

Print the number of positive integers less than or equal to N that have an odd number of digits.

Sample Input 1

11

Sample Output 1

9

Among the positive integers less than or equal to 11, nine integers have an odd number of digits: 1, 2, \ldots, 9.

Sample Input 2

136

Sample Output 2

46

In addition to 1, 2, \ldots, 9, another 37 integers also have an odd number of digits: 100, 101, \ldots, 136.

Sample Input 3

100000

Sample Output 3

90909

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
import java.io.*;
import java.nio.charset.StandardCharsets;

public class Main {

	public static void main(String[] args) throws IOException {
		InputStreamReader reader = new InputStreamReader(System.in, StandardCharsets.UTF_8);
		BufferedReader in = new BufferedReader(reader);

		int N = Integer.parseInt(in.readLine());
		int count = 0;
		if (N <= 9) {
			count = N;
		} else if (N <= 99) {
			count = 9;
		} else if (N <= 999) {
			count = 9 + (N - 99);
		} else if (N <= 9999) {
			count = 9 + (999 - 99);
		} else if (N <= 99999) {
			count = 9 + (999 - 99) + (N - 9999);
		} else {
			count = 9 + (999 - 99) + (99999 - 9999);
		}
		System.out.println(count);
	}
}