input: def dot_product(list1, list2):
      """ Calculate the dot product of two lists.
      >>> dot_product([1, 2], [3, 4])
      11
      >>> dot_product([0, 0], [1, 1])
      0
      """
      product = 0
      for i in range(len(list1)):
          product += (list1[i] * list2[i])
      return product
output:     product = 0
      for i in range(len(list1)):
          product += (list1[i] * list2[i])
      return product