#define red 2
#define yellow 3
#define green 4

void setup()
{
  pinMode(red, OUTPUT);
  pinMode(yellow, OUTPUT);
  pinMode(green, OUTPUT);
}

void loop()
{
  digitalWrite(green, LOW);
  digitalWrite(red, HIGH);
  delay(1000);
  digitalWrite(red, LOW);
  digitalWrite(yellow, HIGH);
  delay(1000);
  digitalWrite(yellow, LOW);
  digitalWrite(green, HIGH);
  delay(1000);
}