code:

void setup() {
  pinMode(13,OUTPUT);
  pinMode(12,OUTPUT);
  pinMode(11,OUTPUT);
  pinMode(10,OUTPUT);
}

const int delay_time=1000; // milliseconds.

void loop() {
  digitalWrite(13,HIGH);
  sleep(delay_time);
  digitalWrite(13,LOW);

  digitalWrite(12,HIGH);
  sleep(delay_time);
  digitalWrite(12,LOW);

  digitalWrite(11,HIGH);
  sleep(delay_time);
  digitalWrite(11,LOW);

  digitalWrite(10,HIGH);
  sleep(delay_time);
  digitalWrite(10,LOW);

}