input: Write a python function to get the day of the week for a given date in the format 'DD-MM-YYYY'.
  assert get_day_of_week("2020-05-15") == 5  # Outputs 5 (Friday)
  assert get_day_of_week("2022-09-21") == 3  # Outputs 3 (Wednesday)
  assert get_day_of_week("2023-01-01") == 6  # Outputs 6 (Sunday)
output: from datetime import datetime
  
  def get_day_of_week(date_str):
      date_obj = datetime.strptime(date_str, "%Y-%m-%d")
      return date_obj.weekday()