const int leds[] = {13,12,11,10,9,8,7,6,5,4,3,2};
void setup() {
  // put your setup code here, to run once:
  for (int i=0; i<12; i++){
    pinMode(leds[i], OUTPUT);
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  for(int i=0; i<12; i+=2){
    digitalWrite(leds[i], HIGH);
    digitalWrite(leds[i+1], HIGH );
    delay(200);
    digitalWrite(leds[i], LOW);
    digitalWrite(leds[i+1],LOW);
  }
}