input: Write a python function to extract the year from a given date string.
  assert get_year_from_date("2023-10-12") == 2023
  assert get_year_from_date("1990-01-01") == 1990
  assert get_year_from_date("2000-12-31") == 2000
output: def get_year_from_date(date_string):
      return int(date_string.split('-')[0])