#define led_red 2
#define led_yellow 0
#define led_green 4
void setup() {
  pinMode(led_red, OUTPUT);
  pinMode(led_yellow, OUTPUT);
  pinMode(led_green, OUTPUT);
}

void loop() {
  //red
 digitalWrite(led_red, HIGH);
 digitalWrite(led_yellow, LOW);
 digitalWrite(led_green, LOW);
 delay(2000);

  //yellow
 digitalWrite(led_red,LOW );
 digitalWrite(led_yellow, HIGH);
 digitalWrite(led_green, LOW);
 delay(2000);

   //green
 digitalWrite(led_red,LOW );
 digitalWrite(led_yellow, LOW);
 digitalWrite(led_green, HIGH);
 delay(2000);
}