int leds[3]={13,12,11};
void setup() {
  // put your setup code here, to run once:
 for (int i=0; i<3;i++){
  pinMode(leds[i], OUTPUT)
 };
}
void loop() {
  // put your main code here, to run repeatedly:
digitalWrite(leds[0],1);
delay(500);
digitalWrite(leds[0],0);
digitalWrite(leds[1],1);
delay(500);
digitalWrite(leds[1],0);
digitalWrite(leds[2],1);
delay(500);
digitalWrite(leds[2],0);
delay(500);
}