text: with open("input") as file:
      lines = file.read().split("\n")
      progs = [line.split(" ")[0] for line in lines]
      references = [r2 for r3 in [r1[1] for r1 in [line.split(" -> ") for line in lines] if len(r1) == 2] for r2 in r3.split(", ")]
      for prog in progs:
          if prog not in references:
              print(prog)
      
  