Lucky Numbers
Time Limit: 0.5 seconds
Memory Limit: 64 megabytes
Description
The numbers of all offices in the new building of the Tax Office of IT City will have lucky numbers.
Lucky number is a number that consists of digits $7$ and $8$ only. Find the maximum number of offices in the new building of the Tax Office given that a door-plate can hold a number not longer than $n$ digits.
Input
The only line of input contains one integer $n$ ($1 ≤ n ≤ 55$) — the maximum length of a number that a door-plate can hold.
Output
Output one integer — the maximum number of offices, than can have unique lucky numbers not longer than $n$ digits.
Examples
Input
2
Output
6