SDUT-OJ1019阿牛的EOF牛肉串

#include<iostream>
using namespace std;
int main()
{
    int n,i;
    long long int a[55];
    a[1] = 3,a[2] = 8;
    while(cin>>n)
    {
    for(i=3;i<=n;i++)
        a[i] = 2 * (a[i-1] + a[i-2]);
    cout<<a[n]<<endl;
    }
return 0;
}