int redLed=12;
int yelowLed=8;
int greenLed=7;


void setup() {
  // put your setup code here, to run once:
pinMode(12, OUTPUT);
pinMode(8, OUTPUT);
pinMode(7, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(redLed, HIGH);
  digitalWrite(yelowLed, LOW);
  digitalWrite(greenLed, LOW);
    delay(3000);
 digitalWrite(redLed, LOW);
  digitalWrite(yelowLed, HIGH);
  digitalWrite(greenLed, LOW);
    delay(1000);
    digitalWrite(redLed, LOW);
  digitalWrite(yelowLed, LOW);
  digitalWrite(greenLed, HIGH);
    delay(3000);
}