Problem:
Score : 200 points

Problem Statement

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.

Sample Input 1

11

Sample Output 1

9

Among the positive integers less than or equal to 11, nine integers have an odd number of digits: 1, 2, \ldots, 9.

Sample Input 2

136

Sample Output 2

46

In addition to 1, 2, \ldots, 9, another 37 integers also have an odd number of digits: 100, 101, \ldots, 136.

Sample Input 3

100000

Sample Output 3

90909

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

n=int(input())
n_str=str(n)
ans=0

if len(n_str)==1:
    print(n)
elif len(n_str) == 2:
    print(9)
elif len(n_str) == 3:
    print(9+n-99)
elif len(n_str) == 4:
    print(900)
elif len(n_str) == 5:
    print(9+900+n-9999)
else:
    print(9+900+90000)