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
from sys import *

n = int(stdin.readline())
ans = 0
for i in range(1, n + 1):
	s = str(i)
	if len(s) % 2 is 1:
		ans += 1 
print(ans)