input: Write a function to calculate the number of elements in a set.
  assert count_elements_in_set({1, 2, 3, 4, 5}) == 5
  assert count_elements_in_set({10, 20, 30, 40}) == 4
  assert count_elements_in_set(set()) == 0
output: def count_elements_in_set(s):
      return len(s)