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)

program main
 implicit none
 integer*8 N,i,j,k
 read(*,*) N
 k = 0
 j = 1
 do i=1,N
  if(j>N) exit
  if(10 <= j .and. j < 100) then 
   j = 100
  else if(1000 <= j .and. j < 10000) then
   j = 10000
  else if(j >= 100000) then
   exit
  else
   j = j+1
   k = k+1
  end if
 end do
 write(*,*) k  
end program main