IndentationError: expected an indented block как исправить?

canvas_width = 700
canvas_height = 500
brush_size = 3
color = "black"
def  paint(event):
  `global brush_size` ошибка на этой строчке
  global color
x1 = event.x - brush_size
x2 = event.x + brush_size
y1 = event.y - brush_size
y2 = event.y + brush_size
w.create_oval(x1, y1, x2, y2, fill = color, outline = color)
def brush_size_change(new_size):
global brush_size
brush_size = new_size
def color_change(new_color):
global color
color = new_color
root = Tk()
root.title('Paint')
w = Canvas(root, width = canvas_width, height = canvas_height, bg = "white")
w.bind("<B1-Motion>", paint)
red_btn = Button(text='Выберете цвет', width=10, command=lambda: color_change(int(input()))
black_btn = Button(text='Черный', width=10, command=lambda: color_change("black"))
green_btn = Button(text='Зеленый', width=10, command=lambda: color_change("green"))
blue_btn = Button(text='Синий', width=10, command=lambda: color_change("blue"))
white_btn = Button(text='Ластик', width=10, command=lambda: color_change("white"))
clear_btn = Button(text='Удалить', width=10, command=lambda: w.delete("all"))
five_btn = Button(text='Выбрать размер кисти', width=20, command=lambda: brush_size_change(int(input('Выберете размер кисти \n'))))
w.grid(row=60, column=0, columnspan=60, padx=5, pady=5, sticky=E+W+S+N)
w.columnconfigure (6, weight=1)
w.rowconfigure (2, weight=1)
red_btn.grid(row=0, column=1)
black_btn.grid(row=0, column=2)
green_btn.grid(row=0, column=3)
blue_btn.grid(row=0, column=4)
white_btn.grid(row=0, column=5)
clear_btn.grid(row=0, column=6, sticky=W)
five_btn.grid(row=1, column=1)
root.mainloop()

как исправить ошибку??