CF630C.Lucky Numbers

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.

IT 城市税务局新办公楼中所有办公室的门牌号都将是幸运号码。

幸运号码是指仅由数字 7 和 8 组成的数字。已知一块门牌最多可容纳长度不超过 $n$ 位的数字，求该税务局新办公楼中办公室的最大数量。

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

输入仅包含一行，其中有一个整数 $n$（$1 ≤ n ≤ 55$）—— 门牌所能容纳的数字的最大长度。

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

输出一个整数——长度不超过 $n$ 位的、互不相同的幸运号码所能分配给的最多办公室数量。