Problem Statement

Two boys, A and B, will share $N$ indistinguishable sweets. How many ways are there to do this so that each boy gets a positive integer number of sweets?

Constraints

• $N$ is an integer.
• $1 \\leq N \\leq 15$

Input

Input is given from Standard Input in the following format:

$N$

Output

Print the answer as an integer.

Sample Input 1

2

Sample Output 1

1

There is only one way to share the sweets: A and B get one sweet each.

Sample Input 2

1

Sample Output 2

0

Sample Input 3

3

Sample Output 3

2