input: Write a function to read in 15 integers and return the sum of them. The function should return 0 if the input list is empty.
  assert sum_nums([1, 5, 9, 0, 2, 4, 7, 8, 6, 10, 3, 11, 12, 13, 14])==105
  assert sum_nums([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1])==15
  assert sum_nums([-1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15])==-120
  assert sum_nums([])==0
output: def sum_nums(nums):
      if not nums:
          return 0
      return sum(nums)