Problem Description

There is a multiple-choice question with $n$ options, and the answer includes at least one option. Due to the obscure nature of the question and its options, you plan to attempt every possible answer to pass this question.

Initially, none of the options are selected. You can perform the following operations any number of times:
- Select an option that is currently not selected.
- Deselect an option that is currently selected.

When the selected options match the answer, you will immediately pass the question. Before starting, you wonder: in the worst case, what is the minimum number of operations required to pass the question?

Input Format

A single line containing an integer $n\ (1\le n \le 20)$, representing the number of options.

Output Format

Output a single integer, which is the minimum number of operations required to pass the question in the worst case.

Sample Input and Output

Sample Input #1

1

Sample Output #1

1

Sample Input #2

2

Sample Output #2

3

Sample Input #3

3

Sample Output #3

7

Sample Input #4

15

Sample Output #4

32767

Notes

The image is unrelated to the problem.

见题面 Input 部分

见题面 Output 部分