303240: CF630C. Lucky Numbers

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Description

Lucky Numbers

题意翻译

给定数字位数,即这个数的位数要小于或者等于它,且这个数字只能由7和8组成,问有多少种情况。

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.

输入输出格式

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

输入样例 #1

2

输出样例 #1

6

Input

题意翻译

给定数字位数,即这个数的位数要小于或者等于它,且这个数字只能由7和8组成,问有多少种情况。

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