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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

public class Main {

  public static void main (String[] args) {

    Scanner sc = new Scanner(System.in);
    
    int N = sc.nextInt();

    sc.close();

    int a = 100000;

    int l = String.valueOf(N).length();

    int ans = 0;

    switch(l){
      case 1:
        ans = N;
      break;
      case 2:
        ans = 9;
      break;
      case 3:
        ans = 9 + N - 99;
      break;
      case 4:
        ans = 909;
      break;
      case 5:
      ans = 909 + N - 9999;
      break;
      case 6:
        ans = 90909;
      break;
    }

    System.out.println(ans);
    
  }

}