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: Accepted)

N = int(input())

lv1 = 10
lv2 = 1000
lv3 = 100000

mod1 = 100
mod2 = 10000

if (N / mod1 < 1):
    if (N < lv1):
        print(N)
    else:
        print(lv1 - 1)
elif (N / mod2 < 1):
    if (N < lv2):
        print(N - (mod1 - 1) + (lv1 - 1))
    else:
        print(lv2 - mod1 + lv1 - 1)
else:
    if (N < lv3):
        print(N - (mod2 - 1) + lv2 - mod1 + lv1 - 1)
    else:
        print(lv3 - mod2 + lv2 - mod1 + lv1 - 1)