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).

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.

Constraints

• $1 \leq N \leq 10^5$

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

见题面 Input 部分

见题面 Output 部分