input: Write a python function to count the number of matching elements between two lists.
  assert count_matches([1, 2, 3], [3, 4, 5]) == 1
  assert count_matches([1, 2, 3, 4], [4, 3, 2, 1]) == 4
  assert count_matches([10, 20, 30], [40, 50, 60]) == 0
output: def count_matches(list1, list2):
      return len(set(list1) & set(list2))