from tkinter import *


def clicked():
    answer = []
    index = 0
    allowed_char = [
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
        'А', 'Б', 'В', 'Г', 'Д', 'Е', 'Ё', 'Ж', 'З', 'И', 'Й', 'К', 'Л', 'М', 'Н', 'О', 'П', 'Р', 'С', 'Т', 'У', 'Ф', 'Х', 'Ц', 'Ч', 'Ш', 'Щ', 'Ъ', 'Ы','Ь', 'Э', 'Ю', 'Я'
    ]
    str1 = txt1.get()
    str2 = txt2.get()
    len_str = len(str1)

    while index < len_str:
        current_char = str1[index]
        if current_char.upper() in allowed_char and current_char in str2 and current_char not in answer:
            answer.append(current_char)
        index += 1

    lbl3.config(text='Ответ: ' + ', '.join(answer))

window = Tk()
window.geometry('400x300')

lbl1 = Label(window, text="Строка 1")
lbl1.grid(column=0, row=0)

lbl2 = Label(window, text="Строка 2")
lbl2.grid(column=0, row=1)

lbl3 = Label(window)
lbl3.grid(column=0, row=3)

txt1 = Entry(window, width=10)
txt1.grid(column=1, row=0)

txt2 = Entry(window, width=10)
txt2.grid(column=1, row=1)

btn = Button(window, text="Старт", command=clicked)
btn.grid(column=0, row=2)

window.mainloop()