http://acm.hdu.edu.cn/showproblem.php?pid=2013
#include <bits/stdc++.h>
using namespace std;
int main()
{
int day;
while(~scanf("%d",&day))
{
int x=1;
day=day-1;
while(day>0)
{
x=(x+1)*2;
day--;
}
printf("%d\n",x);
}
return 0;
}
原文：https://www.cnblogs.com/zlrrrr/p/9321152.html