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 Pascal (FPC 2.6.2) (judge verdict: Accepted)

var n,i,ans :integer;
begin
  ans:=0;
  read(n);
  for i:=1 to n do
    if (i<10)or((i div 100>0)and(i div 100<10))or((i div 10000>0)and(i div 10000<10))
    then inc(ans);
  write(ans);
end.