input: Write a function to find the smallest number in a list.
  assert smallest_list([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]) == 1
  assert smallest_list([10, 20, 4, 45, 99]) == 4
  assert smallest_list([100, 200, 300, 50, 400]) == 50
output: def smallest_list(lst):
      return min(lst)