CodeForces - 630C Lucky Numbers （数学规律）

CodeForces - 630C

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 ndigits.

Sample Input

Input

2

Output

6

Source

Experimental Educational Round: VolBIT Formulas Blitz

#include<stdio.h>
#include<math.h>
#include<string.h>
#include<algorithm>
#define INF 0x3f3f3f3f
#define ll long long
#define N 10010
#define M 1000000007
using namespace std;
ll a[56];
int main()
{
	int i;
	a[1]=2;
	for(i=2;i<=55;i++)
	{
		a[i]=a[i-1]+pow(2,i);
	}
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		printf("%lld\n",a[n]);
	}
	return 0;
}