from machine import Pin
import time

led1 = Pin(27, Pin.OUT)
led2 = Pin(26, Pin.OUT)
led3 = Pin(21, Pin.OUT)

while True:
    led1.value(1)
    time.sleep(1) 

    led1.value(0)
    time.sleep(1)

    led2.value(1)
    time.sleep(1) 

    led2.value(0)
    time.sleep(1)

    led3.value(1)
    time.sleep(1) 

    led3.value(0)
    time.sleep(1)