const int led1 = 3;
const int led2 = 4;
const int led3 = 5;
const int buttonPin = 9;

bool isRunning = false;
bool lastButtonState = HIGH;
unsigned long lastDebounceTime = 0;
unsigned long debounceDelay = 50;
unsigned long previousMillis = 0;
const unsigned long interval = 1000;
int currentLED = 0;

void setup() {
    pinMode(led1, OUTPUT);
    pinMode(led2, OUTPUT);
    pinMode(led3, OUTPUT);
    pinMode(buttonPin, INPUT_PULLUP);
}

void loop() {
    unsigned long currentMillis = millis();
    bool buttonState = digitalRead(buttonPin);

    if (buttonState == LOW && lastButtonState == HIGH && (currentMillis - lastDebounceTime) > debounceDelay) {
        isRunning = !isRunning;
        lastDebounceTime = currentMillis;
    }
    lastButtonState = buttonState;

    if (isRunning && (currentMillis - previousMillis >= interval)) {
        previousMillis = currentMillis;
        updateLEDs();
    }
}

void updateLEDs() {
    digitalWrite(led1, LOW);
    digitalWrite(led2, LOW);
    digitalWrite(led3, LOW);

    if (currentLED == 0) digitalWrite(led1, HIGH);
    else if (currentLED == 1) digitalWrite(led2, HIGH);
    else if (currentLED == 2) digitalWrite(led3, HIGH);
    
    currentLED = (currentLED + 1) % 3;
}