Virtually every single book, play, movie, novel, and game
has at least one character. Most have more, and some even have
thousands! As every good writer knows, the difficulty of
creating a character increases with each new major character
added. This is because fictional characters are truly developed
through their relationships with others.
If there are no characters or only one character, no
relationships need to be explored. With two characters, there
is one relationship. If there are three characters, however,
there are four relationships: the ones between each pair of
characters, and finally the relationship when all three are
together. In general, the relationship between all subsets of
at least two characters must be explored.
Given a literary work with $N$ characters, how many relationships
need to be explored?
Input
The input contains a single integer, $N$ ($0
\leq N \leq 30$), the number of characters.
Output
Output a single line with the number of relationships that
need to be explored.
Sample Input 1 
Sample Output 1 
1

0

Sample Input 2 
Sample Output 2 
3

4
