#define RED 9
#define YELLOW 5
#define GREEN 1
void setup() {
 pinMode(GREEN,OUTPUT);
 pinMode(YELLOW,OUTPUT);
 pinMode(RED,OUTPUT);
}

void loop() {
digitalWrite(GREEN , HIGH);
digitalWrite(RED, LOW);
digitalWrite(YELLOW,LOW);
delay(500);
digitalWrite(GREEN , LOW);
digitalWrite(RED, HIGH);
digitalWrite(YELLOW,LOW);
delay(500);
digitalWrite(GREEN , LOW);
digitalWrite(RED, LOW);
digitalWrite(YELLOW,HIGH);
delay(500);
}