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.*;
import java.io.*;

public class Main {
	private static void solve(){
	//Implement solution here.
		int n = ni();
		int l = String.valueOf(n).length();
		int result = 0;
		if(l == 1) {
			result = n;
		}else if(l == 2){
			result = 9;
		}else if(l == 3) {
			result += 9;
			result += n - 99;
		}else if(l == 4) {
			result = 909;
		}else if(l == 5) {
			result += 909;
			result += n - 9999;
		}else{
			result += 90909;
		}
		
		System.out.println(result);
	}

    //Switch input source (stdin/file)
	private static BufferedReader br  = new BufferedReader(new InputStreamReader(System.in));
	public static void main(String[] args){
        String debugDataPath = System.getenv("DD_PATH");        
        if(debugDataPath != null){
            try{
            	br = new BufferedReader(new InputStreamReader(new FileInputStream(new File(debugDataPath))));
            }catch(Exception e){
                throw new RuntimeException(e);
            }
        } 
        solve();
	}

    //Input read utility
	private static StringTokenizer tokenizer = null;
	public static String next() {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(br.readLine());
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken();
	}
    //Get next single int
	private static int ni() {
		return Integer.parseInt(next());
	}
    //Get next single long
	private static long nl() {
		return Long.parseLong(next());
	}
    //Get next single double
	private static double nd() {
		return Double.parseDouble(next());
	}
    //Get next int array from one line
	private static int[] na(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = ni();
		return a;
	}
	//Get next char array from one line
	private static char[] ns() {
		return next().toCharArray();
	}
    //Get next long array from one line
	private static long[] nal(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nl();
		return a;
	}
}