input: Write a function to return common elements from two sorted lists.
  assert print_common_elements([1, 2, 4, 5, 6], [2, 3, 5, 7]) == [2, 5]
  assert print_common_elements([1, 3, 4, 6], [2, 4, 5, 6]) == [4, 6]
  assert print_common_elements([1, 2, 3], [4, 5, 6]) == []
output: def print_common_elements(list1, list2):
      i, j = 0, 0
      common_elements = []
      
      while i < len(list1) and j < len(list2):
          if list1[i] == list2[j]:
              common_elements.append(list1[i])
              i += 1
              j += 1
          elif list1[i] < list2[j]:
              i += 1
          else:
              j += 1
      
      return common_elements