#define LED1 PA0
#define LED2 PA1
#define LED3 PA2
#define LED4 PA3

void LEDS_off() {
  digitalWrite(LED1, LOW);
  digitalWrite(LED2, LOW);
  digitalWrite(LED3, LOW);
  digitalWrite(LED4, LOW);
}

void LED_on(int led) {
  LEDS_off();
  digitalWrite(led, HIGH);
}

void wait_1s() {
  delay(1000);
}

void setup() {
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(LED3, OUTPUT);
  pinMode(LED4, OUTPUT);
}

void loop() {
  LED_on(LED4);
  wait_1s();

  LED_on(LED3);
  wait_1s();

  LED_on(LED1);
  wait_1s();

  LED_on(LED2);
  wait_1s();
}