import java.util.*;

 import java.math.*;

 public class Main

 {

     public static void main(String[] args)

     {

         Scanner cin = new Scanner(System.in);

         BigInteger a[] = new BigInteger[101];

         a[1] = BigInteger.ONE;

         a[2] = BigInteger.valueOf(3);

         BigInteger Three = BigInteger.valueOf(3);

         for(int i=3; i<=100; i++)

             a[i] = Three.multiply(a[i-1]).subtract(a[i-2]);

         while(cin.hasNext())

         {

             int n = cin.nextInt();

             System.out.println(a[n]);

         }

     }

 }