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 = input()
keta = len(N)

ans = 0
keta_half = keta // 2

if keta_half > 0:
    if keta % 2 == 0:
        for i in range(keta_half):
            ans += 9 * 10 ** (2*i)
    else:
        for i in range(keta_half):
            ans += 9 * 10 ** (2*i)
            zan = int(N[1:]) + 1
            ans += zan
else:
    print("a")
    ans = int(N)

print(ans)