int led[4] = {13, 12, 11, 10};

void setup() {
  // put your setup code here, to run once:
  for(int i = 0; i < 4; i++){
    pinMode(led[i], OUTPUT);
  }
}

void loop() {

for(int j = 0; j < 4; j++){
  digitalWrite(led[j], HIGH);
  delay(500);
  digitalWrite(led[j], LOW);
  delay(300);
}
  
}