def getNumber(prompt):
  while True:
    text = input(prompt)

    if not text:
      return None

    try:
      number = float(text)
      return number
    except ValueError:
      print("It's not a number\n")


def getOperation():
  while True:
    operation = input("Enter the operation (Enter for exit): ")

    if not operation:
      return None

    if operation == '+':
      return a + b

    if operation == '-':
      return a - b

    if operation == '*':
      return a * b

    if operation == '/':
      return a / b

    else:
      print("You've entered the incorrect operation\n")


a = getNumber("Enter the first number (Enter for exit): ")

if a is not None:
  b = getNumber("Enter the second number (Enter for exit): ")

  if b is not None:
    result = getOperation()

    if result is not None:
      print("\nYour result is: ", result)

print("\nSayonara!")