input: Write a python function to calculate the sum of multiples of 4 or 7 up to a given number.
  assert sum_multiples_4_7(100) == 1860
  assert sum_multiples_4_7(50) == 378
  assert sum_multiples_4_7(20) == 84
output: def sum_multiples_4_7(n):
      return sum(x for x in range(n) if x % 4 == 0 or x % 7 == 0)