p02952 AtCoder Beginner Contest 136 - Uneven Numbers
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.

Examples

Input

11


Output

9


Input

136


Output

46


Input

100000


Output

90909
```python
a = int(input())

b = [i for i in range(a) if len(str(i+1))%2!=0]

print(len(b))
```