from utime import sleep
from machine import Pin
red_led = Pin(28, Pin.OUT)
yellow_led = Pin(27, Pin.OUT)
green_led = Pin(26, Pin.OUT)

while True:
    red_led.high()
    sleep(20)
    red_led.low()
    green_led.high()
    sleep(10)
    green_led.low()
    yellow_led.high()
    sleep(2)
    yellow_led.low()