import machine
import time

# Set pin 0 as an output
led = machine.Pin(0, machine.Pin.OUT)

a = 10

# Make your led blink 5 times (=10/2 because toggle)
while a > 0:
    a -= 1           # equivalent to a=a-1
    led.toggle()     # Change LED's status
    time.sleep(0.5)  # Wait for 0.5 seconds