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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

implicit none

integer :: n, m
integer :: i

read *, n

m = 0
do i = 1, n
   if (i < 10) then
      m = m + 1
      cycle
   else if (99 < i .and. i < 1000) then
      m = m + 1
      cycle
   else if (9999 < i .and. i < 100000) then
      m = m + 1
      cycle
   endif
enddo

write(6,'(i0)') m

stop
end