101361: [AtCoder]ABC136 B - Uneven Numbers

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