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=input()
A={1:9, 3:900, 5:90000}
l=len(str(N))

ans=0

for i in range(1,l,2):
	ans+=A[i]

if l%2==1:
	ans+=N-10**(l-1)+1

print ans