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)

a = int(input())
l = len(str(a))

ans = 0
if l % 2 == 0:
    while l >= 1:
        ans += (10 ** (l - 1) - 1) - (10 ** (l - 2) - 1)
        l -= 2
else:
    ans += a - (10 ** (l - 1) - 1) - (10 ** (l - 2) - 1)
    l -= 1
    while l >= 1:
        ans += 10 ** (l - 1) - 1
        l -= 2

print(ans)