input: Write a python function to return the Chinese zodiac sign for the input year.
  assert chinese_zodiac(1997)==('Ox')
  assert chinese_zodiac(1998)==('Tiger')
  assert chinese_zodiac(1994)==('Dog')
output: def chinese_zodiac(year):
      zodiac_signs = ['Rat', 'Ox', 'Tiger', 'Rabbit', 'Dragon', 'Snake', 'Horse', 'Goat', 'Monkey', 'Rooster', 'Dog', 'Pig']
      return zodiac_signs[(year - 4) % 12]