405308: GYM101879 E Group work

Recent studies in Education show great pedagogical benefits of working in groups, especially in the freshman and sophomore years in high school. Different groups of various sizes are great and allow students to understand their differences and to train in teamwork. A teacher at a modern school wants to know how many different groups he can form in this class of $$$N$$$ students. The only requirement is that a group must have at least 2 students, and two groups are distinct if at least one student is in one of them and no in the other.

Your task in this problem is, given $$$N$$$, compute the number of distinct groups that is possible to create in the class.

A single line with an integer $$$N$$$.

Constraints

• $$$1 \leq N \leq 30$$$

A single line with the number of distinct groups that is possible to have in the class.

2

1

3

4

In the first example we have two students, therefore we can only have one group. In the second example we have three students, say $$$A$$$, $$$B$$$ and $$$C$$$. We can form the groups $$$AB$$$, $$$AC$$$, $$$BC$$$ and $$$ABC$$$.