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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;

class ABC
{
    public static void Main()
    {
        string  str = Console.ReadLine();
        List<char> list = new List<char> { };
        foreach(char c in str)
        {
            list.Add(c);
        }

        switch (list.Count) {
            case 1:
                Console.WriteLine(Convert.ToString(list[0]));
                break;
            case 2:
                Console.WriteLine(9);
                break;
            case 3:
                Console.WriteLine(10 +
                    (int.Parse(Convert.ToString(list[0])) - 1) * 100  +
                    int.Parse(Convert.ToString(list[1])) * 10 +
                    int.Parse(Convert.ToString(list[2])));
                break;
            case 4:
                Console.WriteLine(909);
                break;
            case 5:
                Console.WriteLine(10 +
                    (int.Parse(Convert.ToString(list[0])) - 1) * 1000 +
                    int.Parse(Convert.ToString(list[1])) * 100 +
                    int.Parse(Convert.ToString(list[2])) * 10 + 
                    int.Parse(Convert.ToString(list[3])));
                break;
            case 6:
                Console.WriteLine(90909);
                break;
        }
    }
}