#define LED1 1
#define LED2 5
#define LED3 9
#define LED4 13

int leds[] = {LED1, LED2, LED3, LED4};

void setup() {
  for (int i = 0; i < 4; i++) {
    pinMode(leds[i], OUTPUT);
  }
}

void displayNumber(int num) {
  for (int j = 0; j < 4; j++) {
    digitalWrite(leds[j], num & (1 << j) ? HIGH : LOW);
  }
}

void displayComplement(int num) {
  for (int j = 0; j < 4; j++) {
    digitalWrite(leds[j], (~num) & (1 << j) ? HIGH : LOW);
  }
}

void loop() {
  for (int i = 0; i < 16; i++) {
    displayNumber(i);
    delay(1000);
    displayComplement(i);
    delay(1000);
  }
  delay(2000); 
}