CF630C.Lucky Numbers

普及/提高-

通过率：0%

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题目描述

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.

输入格式

The only line of input contains one integer $n$ ( $1<=n<=55$ ) — the maximum length of a number that a door-plate can hold.

输出格式

Output one integer — the maximum number of offices, than can have unique lucky numbers not longer than $n$ digits.

输入输出样例

输入#1
```
2
```
输出#1
```
6
```

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