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-----
11

-----Sample Output-----
9

Among the positive integers less than or equal to 11, nine integers have an odd number of digits: $1, 2, \ldots, 9$.

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