I made a program about caesar cipher but it gives me this error when I am trying to change shift value:

shifted_value = shifted_value + user_input4
^^^^^^^^^^^^^
NameError: name 'shifted_value' is not defined

Code

custom_alphabet = "NİDALQWERTYUIOPĞÜSFGHJKŞZXCVBMÖÇnidalüğpoıuytrewqşkjhgfsçömbvcxz37890712456+=-/%()*$&" 

def three_shift_encrypt(text, alphabet):
    for character in text: #characters contain all of the chars in text
        global shifted_value
        shifted_value = alphabet.find(character) + 3
        print(custom_alphabet[shifted_value], end='')

def three_shift_decrypt(text2, alphabet2):
    for character2 in text2:
        global shifted_value2
        shifted_value2 = alphabet2.find(character2) - 3
        print(custom_alphabet[shifted_value2], end='')

print('To exit the program press Ctrl + C')

while True:
    user_input1 = input('encrypt or decrypt or change shitf value?(e/d/change) -->')
    if user_input1 == 'e':
        user_input2 = input('enter plaintext -->')
        three_shift_encrypt(user_input2, custom_alphabet)
        print('n')
    elif user_input1 == 'd':
        user_input3 = input('enter plaintext -->')
        three_shift_decrypt(user_input3, custom_alphabet)
        print('n')
    elif user_input1 == 'change':
        user_input4 = input('enter the new shift value (int) -->')
        shifted_value = shifted_value + user_input4
        shifted_value2 = shifted_value2 + user_input4
    else:
        print('please enter e or d')
        break

Actually the shifted values ​​were not global. I tried to make it global but it didn’t work.

Why am I getting this error?