const unsigned int LED_PIN = 13;
const unsigned int PAUSE = 700;
const unsigned int FLASH_DURATION = 100;


void flash(int n) {
    for (int i = 0; i < n; i++) {
        digitalWrite(LED_PIN, HIGH);
        delay(FLASH_DURATION);
        digitalWrite(LED_PIN, LOW);
        delay(FLASH_DURATION);
    }
}


void setup() {
    pinMode(LED_PIN, OUTPUT);
}


void loop() {
    for (int i = 1; i < 4; i++) {
        flash(i);
        delay(PAUSE);
    }
    delay(PAUSE);
}