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: Runtime Error)

N = input()
if N < 10:
  print(N)
else:
  if 9 < N < 100:
    print("9")
  else:
    if 99 < N < 1000:
      print(N - 90)
    else:
      if 999 < N < 10000:
        print("909")
      else:
        if 9999 < N < 100000:
          print(909 +  N - 9999)
        else:
          if N = 100000:
            print("90909")