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 $b = 0;

my @list = split(//, $n);
my $t = @list;
my $end = @list/2;

if ($n <= $a){
    if ($t % 2 == 0){
    	print "$end \n";
        }else{
        $end = int($end);
        $end = $end + 1;
        print "$end \n";
        }
    } else {
    print "No \n";
    }