input: Write a function to calculate the sum of all numbers below 1000 that are multiples of 3 or 5.
  assert sum_multiples_3_5(10) == 23
  assert sum_multiples_3_5(100) == 2318
  assert sum_multiples_3_5(1000) == 233168
output: def sum_multiples_3_5(limit):
      return sum(x for x in range(limit) if x % 3 == 0 or x % 5 == 0)