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 = raw_input()

digit_num = len(str(N))
digit_counter = 2
minus_val = 0

while True:
  if digit_counter >= digit_num:
    if digit_num % 2 == 0:
      minus_val += (int(N) - pow(10, digit_num - 1) + 1)
    break
  minus_val += 9 * pow(10, digit_counter - 1)
  digit_counter += 2

print int(N) - minus_val