Score : $100$ points

Problem Statement

How many ways are there to choose two distinct positive integers totaling $N$, disregarding the order?

Constraints

• $1 \leq N \leq 10^6$
• $N$ is an integer.

Input

Input is given from Standard Input in the following format:

$N$

Output

Print the answer.

4

1

There is only one way to choose two distinct integers totaling $4$: to choose $1$ and $3$. (Choosing $3$ and $1$ is not considered different from this.)

999999

499999