Classroom Assignment

Daegu Science High School is repairing its reading hall, so self-study is held in regular classrooms instead. The teachers worried that students would make noise, so they decided to give each class two classrooms. The rooms differ in size, so the teachers rotate the room assignments every day to share them fairly. The school has $N$ classrooms and $\lfloor \frac{N}{2} \rfloor$ classes. Each class is split into students with odd numbers and students with even numbers, and the two groups study in different classrooms.

The first line contains an integer $N$.

Print the maximum number of chocolate pies Jiwoong can receive.

• $2 \le N \le 30$

• The maximum number of chocolate pies Jiwoong can receive does not exceed $2^{60}$.
• If $N$ is odd, one classroom is left empty.
• $\lfloor x \rfloor$ is the greatest integer less than or equal to $x$.