void setup() {
  // put your setup code here, to run once:
pinMode(10, OUTPUT);
pinMode(11, OUTPUT);
pinMode(12, OUTPUT);
pinMode(13, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
int led;
for(led = 10; led<=13; led++){
  digitalWrite(led, HIGH);
  delay(1000);
  digitalWrite(led, LOW);
  delay(1000);
}
for (led=10;led<=13;led++){
  digitalWrite(led, HIGH);
  digitalWrite(led+1, HIGH);
  delay(1000);
  digitalWrite(led, LOW);
  digitalWrite(led+1, LOW);
}
}