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
N = int(raw_input())

digit = len(str(N))

ans  = 0
num = [9, 0, 900, 0, 90000]
if digit%2 == 1:
    ans += sum(num[:digit-1])
    ans += N - 10 ** (digit-1) + 1
else:
    ans += sum(num[:digit-1])

print ans