input: Write a function to calculate the sum of a list containing 15 integers. If the list is not empty, return the sum of the integers. If the list is empty, return 0.
  assert sum_nums([1, 5, 9, 0, 2, 4, 7, 8, 6, 10, 3, 11, 12, 13, 14])==105
  assert sum_nums([])==0
output: def sum_nums(lst):
      if not lst:
          return 0
      return sum(lst)