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 Java (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();

            int count = 0;
            for (int n = 1; n <= N; n++) {
                int mask = 0;
                if (n / 1 > 0) {
                    mask |= (1 << 0);
                }
                if (n / 10 > 0) {
                    mask |= (1 << 1);
                }
                if (n / 100 > 0) {
                    mask |= (1 << 2);
                }
                if (n / 1000 > 0) {
                    mask |= (1 << 3);
                }
                if (n / 10000 > 0) {
                    mask |= (1 << 4);
                }
                if (n / 100000 > 0) {
                    mask |= (1 << 5);
                }

                if ((32 - Integer.numberOfLeadingZeros(mask)) % 2 == 1) {
                    count++;
                }
            }

            System.out.println(count);
        }
    }
}