C - Lucky Numbers-优快云博客

本文介绍了一个算法，用于找出由数字7和8组成的幸运数字的最大数量，这些数字将被用作新税务局大楼办公室门牌号，长度不超过n位。通过递推方式计算所有可能的幸运数字组合，最终输出不超过n位的所有独特幸运数字的数量。

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C - Lucky Numbers

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

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

Output

#include <cstdio>  
#include <cstring>  
#include <cmath>  
#include <cstdlib>  
#include <algorithm>  
#include <queue>  
#include <stack> 
#define INF 0x3f3f3f3f  
#define eps 1e-8   
#define Si(a) scanf("%d", &a)  
#define Sl(a) scanf("%lld", &a)  
#define Sf(a) scanf("%lf", &a)  
#define Ss(a) scanf("%s", a)  
#define Pi(a) printf("%d\n", (a))  
#define Pf(a) printf("%.2lf\n", (a))  
#define Pl(a) printf("%lld\n", (a))  
#define Ps(a) printf("%s\n", (a))  
#define Wi(a) while((a)--)  
#define cle(a, b) memset(a, (b), sizeof(a))  
#define MOD 1000000007  
#define LL long long  
#define PI acos(-1.0) 
using namespace std;
int main()
{
	int n;
	while(Si(n)==1)
	{
		__int64 ans = 0, num = 1;
		for(int i = 1; i <= n; ++i)
		{
			num<<=1;
			ans += num;
		}
		printf("%I64d\n", ans);
	}
	return 0;
}