input: Write a Python function to determine how many negative numbers are in a list.
  assert neg_count([-1, -2, 3, -4, -5]) == 4
  assert neg_count([1, 2, 3]) == 0
  assert neg_count([1, 2, -3, -10, 20]) == 2
output: def neg_count(lst):
      return sum(1 for x in lst if x < 0)