while True:
    
  # read a score from the keyboard (see 5.2.1) 
  grade = input("What is your grade? [A, B, C, D, F, or X to quit]: ")[0] 
  
  if grade == 'X' or grade == 'x': break 
  
  # check for passing grade 
  if grade == 'A' or grade == 'B' or grade == 'C': 
    print("You pass")