Experimental Educational Round: VolBIT Formulas Blitz C

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.

Examples

input

output

6
1位数的，7 8
2位数的，77 78 87 88
3位数的，777 778 787 788 877 878 887 888
.....

#include<stdio.h>

//#include<bits/stdc++.h>

#include<string.h>

#include<iostream>

#include<math.h>

#include<sstream>

#include<set>

#include<queue>

#include<map>

#include<vector>

#include<algorithm>

#include<limits.h>

#define inf 0x7fffffff

#define INF 0x7fffffffffffffff

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define LL long long

#define ULL unsigned long long

using namespace std;

LL  powl(LL x, LL n)

{

    LL pw = 1;

    while (n > 0)

    {

        if (n & 1)        // n & 1 等价于 (n % 2) == 1

            pw *= x;

        x *= x;

        n >>= 1;        // n >>= 1 等价于 n /= 2

    }

    return pw;

}

int main()

{

    LL n;

    LL num;

    cin>>n;

    cout<<powl(2,n+1)-2<<endl;

   // printf("%.20f\n",n*powl(1.000000011,num));

    return 0;

}

巴特西

Experimental Educational Round: VolBIT Formulas Blitz C

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