CodeForces 630C：Lucky Numbers【水】

 Lucky Numbers

Time Limit:500MS     Memory Limit:65536KB     64bit IO Format:%I64d & %I64u

Submit Status

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.

Sample Input

Input

2

Output

6

AC-code:

#include<cstdio>#include<cmath>int main(){int n,i;long long ans=0;scanf("%d",&n);for(i=1;i<=n;i++)ans+=pow(2,i);printf("%lld\n",ans);return 0; }