const int RedLed=13;  //define pin 13
const int YellowLed=14; //define pin 14
const int GreenLed=15; //define pin 15

void setup(){
  pinMode(RedLed, OUTPUT);
  pinMode(YellowLed, OUTPUT);      //define pinmodes
  pinMode(GreenLed, OUTPUT);
}
void loop(){
   digitalWrite(RedLed,HIGH);      //Turn on LED
  delay(100);                     //delay for 1 second
  digitalWrite(RedLed,LOW);        //Turn off LED                   
  delay(100); //delay for 1 second
  digitalWrite(YellowLed,HIGH);
  delay(100);
  digitalWrite(YellowLed,LOW);
  delay(100);
  digitalWrite(GreenLed,HIGH);
  delay(100);
  digitalWrite(GreenLed,LOW);
  delay(100); 
}