input: Write a python function to subtract all elements of a list from the first element in the list.
  assert list_to_number([10, 1, 2, 3, 4]) == 0
  assert list_to_number([100, 20, 30]) == 50
  assert list_to_number([50, 10, 5, 5, 5, 5]) == 20
output: def list_to_number(lst):
      return lst[0] - sum(lst[1:])