#define BTN_PIN PA1

#define LED1 PA4
#define LED2 PA5
#define LED3 PA6

int state = 0;

unsigned long lastScan = 0;
bool lastBtn = HIGH;

void setLEDs(int s) {
  digitalWrite(LED1, (s == 0) ? HIGH : LOW);
  digitalWrite(LED2, (s == 1) ? HIGH : LOW);
  digitalWrite(LED3, (s == 2) ? HIGH : LOW);
}

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

  pinMode(BTN_PIN, INPUT_PULLUP); // button to GND

  setLEDs(state); // start with LED1 ON
}

void loop() {
  // Scan only every 20ms (VERY CPU friendly)
  if (millis() - lastScan < 20) return;
  lastScan = millis();

  bool btn = digitalRead(BTN_PIN);

  // Detect press edge: HIGH -> LOW
  if (lastBtn == HIGH && btn == LOW) {
    state++;
    if (state > 3) state = 0;
    setLEDs(state);
  }

  lastBtn = btn;
}