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.Linq;
using System.Text;
using System.Threading.Tasks;



class Program
{
    const int MOD = 1000000007;
    const int INF = 1 << 30;

    static void Main(string[] args)
    {
        Solve();
    }

    static void Solve()
    {
        Scaner sc = new Scaner();
        write wr = new write();

        int N=sc.Int1;
        int ans=0;
        for(int i=1;i<=N;++i){
            string x=i.ToString();
            if(x.Length%2==1){
                ans++;
            }
        }
    wr.wri(ans);

    }
}





class Scaner
{
    public string Str => Console.ReadLine();

    public string[] StrArr => Str.Split(' ');

    public long[] LongArr => StrArr.Select(long.Parse).ToArray();
    public int[] IntArr => StrArr.Select(int.Parse).ToArray();
    public char[] CharArr => Str.ToArray();
    public long Long1 => LongArr[0];
    public int Int1 => IntArr[0];
    
}



class write
{
    public  void wri<T>(T x)
    {
        Console.WriteLine(x);
    }
}