input: Write a python function to calculate the number of negative integers 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)