1 import java.util.*; 2 import java.math.*; 3  4 public class Main 5 { 6     public static void main(String[] args)  7     { 8         Scanner cin = new Scanner(System.in); 9         BigInteger a[] = new BigInteger[101];10         a[1] = BigInteger.ONE;11         a[2] = BigInteger.valueOf(3);12         BigInteger Three = BigInteger.valueOf(3);13         for(int i=3; i<=100; i++)14             a[i] = Three.multiply(a[i-1]).subtract(a[i-2]);15         while(cin.hasNext())16         {17             int n = cin.nextInt();18             System.out.println(a[n]);19         }20     }21 }