const int led1 = 3;
const int led2 = 5;
const int buzzer = 9;

void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(buzzer, OUTPUT);
}

void loop() {

    digitalWrite(led1, HIGH);
    digitalWrite(led2, LOW);
    tone(buzzer, 600);
    delay(300);

    digitalWrite(led1, LOW);
    digitalWrite(led2, HIGH);
    tone(buzzer, 1200);
    delay(300);
}