void setup() {
pinMode(7, OUTPUT);
pinMode(8, OUTPUT);
pinMode(12, OUTPUT);
pinMode(13, OUTPUT);

}

void loop() {
digitalWrite(7,HIGH);
delay(500);
digitalWrite(7,LOW);
digitalWrite(8,HIGH);
delay(500);
digitalWrite(8,LOW);
digitalWrite(12,HIGH);
delay(500);
digitalWrite(12,LOW);
digitalWrite(13,HIGH);
delay(500);
digitalWrite(13,LOW);

}