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())
if n < 10:
    print(n)
elif n >= 10 and n < 100:
    print(9)
elif n >=100 and n < 1000:
    print((n-100) + 10)#n-90
elif n >=1000 and n < 10000:
    print(909)
elif n >= 10000 and n < 100000:
    print((n-10000) + 910)
elif n == 100000:
    print(90909)