void setup() {
  // put your setup code here, to run once:
  pinMode(2, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(7, INPUT_PULLUP);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(7) == 0){
    digitalWrite(2, HIGH);
    digitalWrite(4, LOW);
    delay(300);
    digitalWrite(2, LOW);
    digitalWrite(4, HIGH);
    delay(300);
  }
  else{
    digitalWrite(2, LOW);
    digitalWrite(4, LOW);    
  }
}