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 Go (1.6) (judge verdict: Accepted)

package main

import (
	"fmt"
	"strconv"
)

func main() {
	var n string
	fmt.Scan(&n)
	nInt, _ := strconv.Atoi(n)
	ans := 0
	for i:=1; i<nInt+1; i++ {
		if i < 10 {
			ans++
		} else if 99 < i && i < 1000 {
			ans++
		} else if 9999 < i && i < 100000 {
			ans++
		}
	}
	fmt.Println(ans)
}