int green = 2;
int yellow = 4;
int red = 7;

void setup() {
  // put your setup code here, to run once:
pinMode(green, OUTPUT);
pinMode(yellow, OUTPUT);
pinMode(red, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(green, LOW);
  digitalWrite(red, HIGH);
  delay(1000);
  digitalWrite(yellow, HIGH);
  delay(1000);
  digitalWrite(red, LOW);
  digitalWrite(yellow, LOW);
  digitalWrite(green, HIGH);
  delay(1000);
  digitalWrite(green, LOW);
  digitalWrite(yellow, HIGH);
  delay(1000);
  digitalWrite(yellow, LOW);
}