void setup()
{
// initialize digital pin 2 as an output
pinMode(2, OUTPUT);
pinMode(4, OUTPUT);
pinMode(7, OUTPUT);
pinMode(13, OUTPUT);
}
// the loop function runs over and over again forever
void loop()
{
 digitalWrite(13, HIGH); // turn the LED1 on
 digitalWrite(2, LOW); //turn the LED2 off
 digitalWrite(7, HIGH); // turn the LED3 on
 digitalWrite(4, LOW); //turn the LED4 off
 delay(3000); // wait for a second
 digitalWrite(13, HIGH); // turn the LED1 on
 digitalWrite(2, HIGH); //turn the LED2 on
 digitalWrite(7, LOW); //turn the LED3 off
 digitalWrite(4, LOW); //turn the LED4 off
 delay(3000); // wait for a second
 digitalWrite(13, HIGH); // turn the LED1 on
 digitalWrite(2, LOW); //turn the LED2 off
 digitalWrite(7, LOW); //turn the LED3 off
 digitalWrite(4, HIGH); //turn the LED4 on
 delay(3000); // wait for a second
 digitalWrite(13, HIGH); // turn the LED1 on 
 digitalWrite(2, LOW); //turn the LED2 off
 digitalWrite(7, HIGH); // turn the LED3 on
 digitalWrite(4, HIGH); //turn the LED4 on
 delay(3000); // wait for a second
}