input: Write a function to convert Fahrenheit to Celsius.
  assert Fahrenheit_to_Celsius(32) == 0
  assert Fahrenheit_to_Celsius(100) == 37.77777777777778
  assert Fahrenheit_to_Celsius(0) == -17.77777777777778
output: def Fahrenheit_to_Celsius(fahrenheit):
      return (fahrenheit - 32) * 5 / 9