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 (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var (
	read  = bufio.NewReader(os.Stdin)
	write = bufio.NewWriter(os.Stdout)
)

func min(a, b int) int {
	if a <= b {
		return a
	}
	return b
}

func max(a, b int) int {
	if a >= b {
		return a
	}
	return b
}

func yesno(result bool) {
	if result {
		fmt.Fprintln(write, "Yes")
	} else {
		fmt.Fprintln(write, "No")
	}
}

func printansStr(result bool, a, b string) {
	if result {
		fmt.Fprintln(write, a)
	} else {
		fmt.Fprintln(write, b)
	}
}

func printansInt(result bool, a, b int) {
	if result {
		fmt.Fprintln(write, a)
	} else {
		fmt.Fprintln(write, b)
	}
}

func main() {
	defer write.Flush()

	var n int
	fmt.Fscan(read, &n)

	cnt := 0
	for i := 1; i <= n; i++ {
		if len(strconv.Itoa(i))%2 == 1 {
			cnt++
		}
	}
	fmt.Fprintln(write, cnt)
}