B - Uneven Numbers /

制約

• 1 \leq N \leq 10^5

入力

N


出力

N 以下の正の整数のうち、桁数が奇数であるようなものの個数を出力せよ。

入力例 1

11


出力例 1

9


11 以下の正の整数のうち、桁数が奇数であるようなものは 1, 2, \ldots, 99 個です。

入力例 2

136


出力例 2

46


1, 2, \ldots, 9 に加えて、100, 101, \ldots, 13637 個の数も桁数が奇数です。

入力例 3

100000


出力例 3

90909


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