from tkinter import *

from tkinter.messagebox import showerror

def countup():

   global enta, result, btn, entb

   try:

       a = int(enta.get())

       b = int(entb.get())

   except: return showerror("Error window...", "Something went wrong...")

   return result.configure(text = "Answer: " + str(a*(4*b - a)))

root = Tk()

root.title("Ivan Ivanovich")

root.geometry("400x300")

ta = StringVar()

result = Label(master=root, text="No operations", bg="yellow")

enta = Entry(master=root, text="ff", textvariable=ta, bd=5, bg="lightyellow")

entb = Entry(master=root, text="ff", bd=5, bg="lightyellow")

btn = Button(master=root, text="Count up", command=countup)

result.pack()

Label(master=root, text="Input a:", font=("Courier", 9, "italic")).pack()

enta.pack()

Label(master=root, text="Input b:", font=("Courier", 9, "italic")).pack()

entb.pack()

btn.pack()

root.mainloop()