Problem Statement 
 Return how many strings containing length characters do not have the substring (quotes for clarity) "ab". The only characters allowed in the strings are 'a', 'b', and 'c'. A substring is any contiguous portion of a string. A substring may be empty, or the entire string. 

Definition 
 Class:  BadSubstring  Method:  howMany  Parameters:  int  Returns:  long  Method signature:  long howMany(int length)  (be sure your method is public) 




Constraints 
  length will be between 0 and 44 inclusive. 

Examples 
0)  
  Returns: 1  The only string of length 0 is the empty string, and it doesn't have "ab" as a substring. 


1)  
  Returns: 21  There are 3*3*3=27 possible strings of length 3. 3 begin with ab, and 3 end with ab. The remaining 21 are all good. 


2)  
 