code: def get_id(page):
    
    start_pos = page.find("<id>")
    end_pos = page.find("</id>")
    assert start_pos != -1
    assert end_pos != -1
    start_pos += len("<id>")
    return int(page[start_pos:end_pos])
docs: Extract the id from a page.
  
    Args:
      page: a string
    Returns:
      an integer