new_contents: number_list = input().strip()
  
  minus_position = number_list.find('-1')
  
  if -1 == number_list.find('-1'):
      exit()
  
  number_list = number_list[:minus_position].strip().split()
  
  summation = 0
  
  for number in number_list:
      summation += int(number) 
  
  print(summation / len(number_list))
  
subject: Add average of integers