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.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int ans = 0;
		int i = 0;
		while(true) {
			int div = n / (int) Math.pow(10, i);
			int mod = n % (int) Math.pow(10, i);
			if(div >= 10) {
				ans += Math.pow(10, i) * 9;
			} else if(div > 0) {
				ans += (div - 1) * Math.pow(10, i);
				ans += mod + 1;
				break;
			} else {
				break;
			}
			i += 2;
		}
		System.out.println(ans);
	}

}