#!/usr/bin/python3
import RPi.GPIO as GPIO
import time

leds = [ 21, 16, 19 ] 

def setup():
    GPIO.setmode(GPIO.BCM)
    for led_pin in leds:
        GPIO.setup(led_pin, GPIO.OUT)
     
def led_on(led_pin):
    GPIO.output(led_pin, GPIO.HIGH)

def led_off(led_pin):
    GPIO.output(led_pin, GPIO.LOW)
    
def main():
    speed = int(input("Speed in milliseconds? ")) / 1000.0
    
    try:
        setup()
        while True:
            for led in leds:
                led_on(led)
                time.sleep(speed)
                led_off(led)
    finally:
        for led in leds:
            led_off(led)
        GPIO.cleanup

main()