Snake game part 4 problem

import turtle
import time
import random
import math

wn = turtle.Screen()
wn.setup(height=1000, width=1000)
wn.bgcolor("grey")
wn.title("Snake by @a_busy_coding_nerd")
wn.tracer(0)

delay = (0.00001)

border_pen = turtle.Turtle()
border_pen.penup()
border_pen.hideturtle()
border_pen.speed("fastest")
border_pen.goto(-400, -400)
border_pen.pendown()
border_pen.pensize(6)
for square in range(4):
    border_pen.fd(800)
    border_pen.left(90)

speed = 3
score = 0
lives = 1

snake = turtle.Turtle()
snake.shape("square")
snake.color("green")
snake.penup()
snake.shapesize(stretch_wid=1, stretch_len=1)
snake.speed(0)
snake.goto(0,0)
snake.setheading(90)

apple = turtle.Turtle()
apple.shape("circle")
apple.color("red")
apple.penup()
apple.shapesize(stretch_wid=1, stretch_len=1)
apple.speed(0)
apple.goto(0, 300)

pen = turtle.Turtle()
pen.hideturtle()
pen.penup()
pen.goto(0,460)
pen.color("black")
pen.write("Your lives: 1",align="center",font=("Courier",24,"bold"))

pen1 = turtle.Turtle()
pen1.hideturtle()
pen1.penup()
pen1.goto(0,430)
pen1.color("black")
pen1.write("Your score: 0",align="center", font=("Courier",24,"bold"))

pen2 = turtle.Turtle()
pen2.hideturtle()
pen2.penup()
pen2.goto(0,60)
pen2.color("black")

snake_body_parts = []

def snake_up():
    snake.setheading(90)

def snake_right():
    snake.setheading(0)

def snake_left():
    snake.setheading(180)

def snake_down():
    snake.setheading(270)

wn.listen()
wn.onkey(snake_up,"Up")
wn.onkey(snake_right,"Right")
wn.onkey(snake_left,"Left")
wn.onkey(snake_down,"Down")



while True:
    wn.update()

    snake.fd(speed)

    if snake.ycor() > 400 or snake.ycor() < -400:
        lives -= 1

    if snake.xcor() > 400 or snake.xcor() < -400:
        lives -= 1

    if lives == 0:
        apple.hideturtle()
        pen.clear()
        pen1.clear()
        pen1.goto(0,0)
        pen1.write("Your score: {}".format(score),align="center", font=("Courier",24,"bold"))
        pen2.write("Game over!",align="center", font=("Courier",24,"bold"))

    d = math.sqrt(math.pow(snake.xcor()-apple.xcor(),2) + math.pow(snake.ycor()-apple.ycor(),2))

    if d < 20:
        x = random.randint(-390, 390)
        y = random.randint(-390, 390)
        apple.goto(x, y)
        score += 1
        pen1.clear()
        pen1.write("Your score: {}".format(score),align="center", font=("Courier",24,"bold"))

        new_snake_part = turtle.Turtle()
        new_snake_part.penup()
        new_snake_part.shape("square")
        new_snake_part.color("lightgreen")
        new_snake_part.speed(0)
        snake_body_parts.append(new_snake_part)

    for index in range(len(snake_body_parts)-1, 0, -1):
        x = snake_body_parts[index-1].xcor()
        y = snake_body_parts[index-1].ycor()
        snake_body_parts[index].goto(x, y)

    if len(snake_body_parts) > 0:
        x = snake.xcor()
        y = snake.ycor()
        snake_body_parts[0].goto(x, y)

    time.sleep(delay)

wn.mainloop()