Input..........Output  
=====================
  A ..................A  
  B...................A  
  AB..................B  
  ABC.................C  
  CAT.................C  
  DOG.................C  
  DOVE................D  
  QUEUE...............E  
  FEMALE..............F  
  QUESTION............H  
  WHAT................?  
  IS..................?  
  ZODIAC..............?  
  ?...................I  
  ?...................F