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 < 100:
    print 9
elif n < 1000:
    print (n - 90)
elif n < 10000:
    print 909
elif n < 100000:
    print (n-90-9000)
else:
    print 90909
