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: Accepted)

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
class Program
{
    static int x;
    static List<int> s = new List<int>();
    static string result;
    static void Main()
    {
        string tmp = Console.ReadLine();
        x=int.Parse(tmp);
        int results=0;
        for (int i = 1; i <=x; i++) { if (i / 100000 >0) { } else { if (i / 10000 > 0) { results++; } else { if (i / 1000 > 0) { } else { if (i / 100 > 0) { results++; } else { if (i / 10 > 0) { } else { results++; } } } } } }
        result =results.ToString();
            Console.WriteLine(result);
            Console.Out.Flush();
        
    }

 


}