import tkinter

tmr=180
def count_up():
    global tmr
    global after_id
    tmr = tmr -1
    if tmr >= 0:
        label["text"]=tmr
    after_id=root.after(1000,count_up)
def click_btn():
    global tmr
    global after_id
    label["text"]=tmr - 1
    root.after(1000,count_up)
def click_btn2():
    button["text"]="Start"
    global after_id
    root.after_cancel(after_id)
def click_btn3():
    root.quit()
def click_btn4():
    global tmr
    tmr= 180
    label["text"]=tmr
    

    
    

    


root = tkinter.Tk()
label = tkinter.Label(text="180",font=("Ties New Roman",20))
label.pack()
button = tkinter.Button(text="Start",font=("Times New Roman",32), bg="green",command=click_btn)
button2 = tkinter.Button(text="Stop",font=("Times New Roman",32), bg="green",command=click_btn2)
button3 = tkinter.Button(text="Quit",font=("Times New Roman",32), bg="green",command=click_btn3) 
button4 = tkinter.Button(text="Reset",font=("Times New Roman",32), bg="green",command=click_btn4) 
button.pack()
button2.pack()
button3.pack()
button4.pack()
root.mainloop()