// Blink LED on PC13 (Onboard Blue Pill LED)
void setup() {
  pinMode(PB0, OUTPUT); // Set PC13 (onboard LED) as output
}

void loop() {
  digitalWrite(PB0, LOW);  // Turn LED ON (active-low)
  delay(500);               // Delay 500 milliseconds
  digitalWrite(PB0, HIGH); // Turn LED OFF
  delay(500);               // Delay 500 milliseconds
}