Contest Duration: - (local time) (100 minutes) Back to Home
B - Uneven Numbers /

Time Limit: 2 sec / Memory Limit: 1024 MB

### 制約

• 1 \leq N \leq 10^5

### 入力

N


### 出力

N 以下の正の整数のうち、桁数が奇数であるようなものの個数を出力せよ。

### 入力例 1

11


### 出力例 1

9


11 以下の正の整数のうち、桁数が奇数であるようなものは 1, 2, \ldots, 99 個です。

### 入力例 2

136


### 出力例 2

46


1, 2, \ldots, 9 に加えて、100, 101, \ldots, 13637 個の数も桁数が奇数です。

### 入力例 3

100000


### 出力例 3

90909


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