#my function

def common_elements(a_dict):

    empty_list = [  ]

    for key, value in a_dict.items( ):

        if key in a_dict.keys( ) and key in a_dict.values( ):   #if an element is both a value and key

            empty_list.append(key)

    print(empty_list)


my_dict = {
    "A": "K",
    "B": "D",
    "C": "A",
    "D": "Z"
}                                   #Sample dictionary

common_elements(my_dict)                                                                                      #This would return A and D because both A and D are values and keys in my_dict dictionary