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.
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 one integer — the maximum number of offices, than can have unique lucky numbers not longer than n digits.
2
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;
}
Experimental Educational Round: VolBIT Formulas Blitz C
原文：http://www.cnblogs.com/yinghualuowu/p/5208367.html