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)

# -*- coding: utf-8 -*-
N = int(input())
if N == 100000:
  x = 90909
elif N >= 10000:
  x = 909 + N - 10000 + 1
elif N >= 100:
  if N >= 1000:
    x = 909
  else:
    x = 9 + N - 100 + 1
elif N >= 1:
  if N >= 10:
    x = 9
  else:
    x = N
    
print(x)