Problem Description

If an integer, when read from the lowest digit to the highest digit, has odd digits in odd positions (ones, hundreds, ten-thousands, ...) and even digits in even positions (tens, thousands, hundred-thousands, ...), then we call it a "good number".

Given a positive integer $N$, compute how many good numbers there are from $1$ to $N$.

Input Format

An integer $N$.

Output Format

An integer representing the answer.

24

7

2024

150

Hint

Explanation for Sample 1

The good numbers within $24$ are $1,3,5,7,9,21,23$, for a total of $7$.

Constraints

• For $10\%$ of the testdata, $1 \leq N \le 100$.
• For all testdata, $1 \le N \leq 10^7$.

Translated by ChatGPT 5