hdu 2047

 

#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
    int n;
    while(cin>>n)
    {
       __int64 A[41][2]={{0,0},{1,2}};      //注意下__int64
       for(int i=2;i<41;i++)
       {
           A[i][0]=A[i-1][1];
           A[i][1]=2*(A[i-1][0]+A[i-1][1]);     
              
              
              
               }
       cout<<A[n][0]+A[n][1]<<endl;                 
                
                
                
                
                
                 }
   
   
   
   
   
   // system("PAUSE");
    return EXIT_SUCCESS;
}