void setup() {
  // put your setup code here, to run once:

  for(int i = 4; i <= 7; i++){
    pinMode(i, OUTPUT);
  } 

}

void loop() {
  // put your main code here, to run repeatedly:

  for(int i = 4; i <= 7; i++){
    digitalWrite(i, HIGH);
    delay(500);
  } 

  for(int i = 4; i <= 7; i++){
    digitalWrite(i, LOW);
    delay(500);
  } 

}