# example1.py
# a program that takes all decimal values until a user enters a
# negative number and fins their average.

def main():

  print("This program collects all values until the user \
enters a negative value, then returns average of all non-negative values.")

  x, s, counter = 0, 0, -1

  while x >= 0:
    s += x
    counter += 1

    try:
      x = float(input("Enter a value:"))
      
    except:
      print("invalid input")
      break;

  if counter > 0:
    print("You entered {0} non-negative values, their average is {1}.".format(counter,s/counter))
  else:
    print("you didn't enter any non-negative values")

main()