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"
	"os"
	"strconv"
	"fmt"
)

var sc = bufio.NewScanner(os.Stdin)
var ReadString func() string
var ReadLine func() string
var ReadInt64 func() int64
var ReadInt func() int
var ReadIntSlice func(int) []int
var ReadInt64Slice func(int) []int64
var GetIntAbs func(int) int
var Atoi func(string) int
var FindMin func([] int) int
var FindMax func([] int) int
var StrReverse func(string) string

func init() {
	ReadString = newReadString()
	ReadLine = readLine
	ReadInt64 = readInt64
	ReadInt = readInt
	ReadIntSlice = readIntSlice
	FindMin = findMin
	FindMax = findMax
	StrReverse = strReverse
  GetIntAbs = getIntAbs
}

func main() {
	n := ReadInt()
  var ans int
  for i := 1; i <= n; i++ {
    s := len(strconv.Itoa(i))
    if s % 2 == 1 {
      ans++
    }
  }
  fmt.Println(ans)
}

func strReverse(s string) string {
	runes := []rune(s)
	l := len(runes)
	for i, j := 0, l-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}


func newReadString() func() string {
	sc.Buffer(make([]byte, 1024), 2048)
	sc.Split(bufio.ScanWords)
	return func() string {
		if !sc.Scan() {
			panic("scanできなかった")
		}
		return sc.Text()
	}
}

func readLine() string {
	if !sc.Scan() {
		panic("line をscanできなかった")
	}
	return sc.Text()
}

func readInt64() int64 {
	i, err := strconv.ParseInt(ReadString(), 0, 64)
	if err != nil {
		fmt.Println("parseInt失敗")
		panic(err.Error())
	}
	return int64(i)
}

func readInt() int {
	i := ReadInt64()
	return int(i)
}

func readIntSlice(n int) []int {
	arr := make([]int, n)
	for i := 0; i < n; i++ {
		arr[i] = ReadInt()
	}
	return arr
}

func readInt64Slice(n int) []int64 {
	arr := make([]int64, n)
	for i := 0; i < n; i++ {
		arr[i] = ReadInt64()
	}
	return arr
}

/*------ number util ------*/

func getIntAbs(n int) int {
	if n < 0 {
		return -n
	}
	return n
}

func atoi(a string) int {
	i, err := strconv.Atoi(a)
	if err != nil {
		panic(err.Error())
	}
	return i
}

func findMin(arr []int) int {
	if len(arr) == 0 {
		return 0
	}
	min := arr[0]
	for _, v := range arr {
		if v < min {
			min = v
		}
	}
	return min
}

func findMax(arr []int) int {
	if len(arr) == 0 {
		return 0
	}
	max := arr[0]
	for _, v := range arr {
		if v > max {
			max = v
		}
	}
	return max
}