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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php 
	$n = fgets(STDIN);
	$count = 0;
	if ($n > 9999) {
      $count += $n-9801;
    }
	if ($n > 99 && $n < 1000) {
      $count += $n-90;
    }
	if ($n > 10 && $n < 100) {
      $count += 9;
    }
	echo $count;
?>