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 Scala (2.11.7) (judge verdict: Accepted)

import java.util.Scanner

object Main extends App {
  val sc = new Scanner(System.in)

  val n = sc.nextInt

  val res = n match{
    case x if x <= 9 => x
    case x if x <= 99 => 9
    case x if x <= 999 => 9 + (x - 100 + 1)
    case x if x <= 9999 => 9 + 900
    case x if x <= 99999 => 9 + 900 + (x - 10000 + 1)
    case x if x <= 100000 => 9 + 900 + 90000
  }

  println(res)

}