input: 
  def store_integers(lst: List[int]) -> IntList:
      """Store a list of integers in a custom data structure IntList and return it.
      >>> store_integers([3, 1, 4, 1, 5, 9])
      IntList([3, 1, 4, 1, 5, 9])
      >>> store_integers([])
      IntList([])
      """
  
output:     return IntList(lst)