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())
 
ans = 0
 
if n >= 10:
  ans += 10 - 1
  if n >= 10**2:
    if n >= 10**3:
      ans += 10**3 - 10**2
      if n >= 10**4:
        if n == 10**5:
          ans += 10**5 - 10**4
        else:
          ans += n - 10**4 + 1
    else:
      ans += n - 10**2 + 1
else:
  ans += n
 
print(ans)