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?

Input

Input is given from Standard Input in the following format:
N

Output

Print the answer as an integer.

Constraints

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

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

见题面 Input 部分

见题面 Output 部分