C - Doubled

Score : $300$ points

Problem Statement

Given is an integer $N$.
How many integers $x$ between $1$ and $N$ (inclusive) satisfy the following condition?

• The decimal representation (without leading zeros) of $x$ has an even number of digits, and its first and second halves are equal as strings.

Constraints

• $N$ is an integer.
• $1 ≤ N < 10^{12}$

Input

Input is given from Standard Input in the following format:

$N$

Output

Print the answer.

33

3

Three numbers $11$, $22$, and $33$ satisfy the condition.

1333

13

For example, the decimal representation of $1313$ has four digits, and its first and second halves are both $13$, so $1313$ satisfies the condition.

10000000

999