const int buttonPins[] = {2, 3, 4, 5};  
const int relayPin = 8;  
const int relayActivateTime = 4000;  // 4 seconds

unsigned long lastActivationTime = 0;
int lastPressedButton = -1;

void setup() {
  Serial.begin(115200);
  pinMode(relayPin, OUTPUT);

  for (int i = 0; i < 4; ++i) {
    pinMode(buttonPins[i], INPUT_PULLUP);
  }
}

void loop() {
  for (int i = 0; i < 4; ++i) {
    if (digitalRead(buttonPins[i]) == LOW) {
      // Button is pressed
      if (i != lastPressedButton) {
        Serial.print("Button ");
        Serial.println(i);
        // Button is different from the last one pressed
        activateRelay();
        lastPressedButton = i;
      }
    }
  }
}

void activateRelay() {
  digitalWrite(relayPin, HIGH);  
  delay(relayActivateTime);
  digitalWrite(relayPin, LOW);  
  lastActivationTime = millis();  
  lastPressedButton = -1; 
}