from machine import Pin
from time import sleep, sleep_ms
led1=Pin(18,Pin.OUT)
led2=Pin(19,Pin.OUT)
led3=Pin(20,Pin.OUT)
led4=Pin(21,Pin.OUT)
while True:
    led1.high()
    sleep_ms(600)
    led1.low()
    led2.high()
    sleep_ms(600)
    led2.low()
    led3.high()
    sleep_ms(600)
    led3.low()
    led4.high()
    sleep_ms(600)
    led4.low()