算法之路三：HDU OJ:2013

#include<cstdio>
#include<iostream>
using namespace std;

const int maxn=40;

int main()
{
    int a[maxn]={0};
    int n;
    while(cin>>n&&n)
    {
        a[n]=1;
        for(int i=n;i>=1;i--)
        a[i-1]=2*a[i]+2;
        cout<<a[1]<<endl;
    }
    return 0;
}