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 Perl (v5.18.2) (judge verdict: Wrong Answer)

my $n = <STDIN>;

my $a = 10*10*10*10*10;
my $count = 0;

if ($n <= 99){
 if ($n < 10){
	while ($count < $n){
 		$count = $count + 1;
    }
 }else{
 	$count = 9;
 }
}else{
	if ($n > 99 && $n <= 9999){
    	if ($n < 1000){
    		$count2 = 100;
	    	while ($count2 < $n){
 				$count = $count + 1;
 				$count2 = $count2 + 1;
   			}
            $count = $count + 9;
		}else{
 			$count = 9*9*9 + 9;
 		}
	}else{
	if ($n > 9999 && $n <= 999999){
    	if ($n < 100000){
    		$count3 = 10000;
	    	while ($count3 < $n){
 				$count = $count + 1;
 				$count3 = $count2 + 1;
   			}
            $count = $count + 9*9*9;
		}else{
 			$count = 9*9*9*9*9 + 9*9*9 + 9;
 		}
	}
}
}
print "$count \n";